full bore safety valve working principle quotation

(WIRE DRAWING– IT IS THE CONDITION IN WHICH A THIN FILM OF STEAM BLOWS ACROSS BETWEEN THE VALVE FACES CAUSING THE CUTTING OF THE VALVE FACES WHICH LEADS TO THE LOSS OF THE VALVE STEAM.)

3.WHEN THE STEAM ACTS ON THE OPERATING PISTON IT CAUSES THE OPENING OF THE MAIN VALVE AGAINST THE SPRING PRESSURE. AS THE DIAMETER IS TWICE OF THE MAIN VALVE IT CAUSE THE D/4 LIFTING OF THE MAIN VALVE(i:e- FULL LIFT OF THE SAFETY VALVE).

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A safety valve is a valve that acts as a fail-safe. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds preset limits. Pilot-operated relief valves are a specialized type of pressure safety valve. A leak tight, lower cost, single emergency use option would be a rupture disk.

Safety valves were first developed for use on steam boilers during the Industrial Revolution. Early boilers operating without them were prone to explosion unless carefully operated.

Vacuum safety valves (or combined pressure/vacuum safety valves) are used to prevent a tank from collapsing while it is being emptied, or when cold rinse water is used after hot CIP (clean-in-place) or SIP (sterilization-in-place) procedures. When sizing a vacuum safety valve, the calculation method is not defined in any norm, particularly in the hot CIP / cold water scenario, but some manufacturers

The earliest and simplest safety valve was used on a 1679 steam digester and utilized a weight to retain the steam pressure (this design is still commonly used on pressure cookers); however, these were easily tampered with or accidentally released. On the Stockton and Darlington Railway, the safety valve tended to go off when the engine hit a bump in the track. A valve less sensitive to sudden accelerations used a spring to contain the steam pressure, but these (based on a Salter spring balance) could still be screwed down to increase the pressure beyond design limits. This dangerous practice was sometimes used to marginally increase the performance of a steam engine. In 1856, John Ramsbottom invented a tamper-proof spring safety valve that became universal on railways. The Ramsbottom valve consisted of two plug-type valves connected to each other by a spring-laden pivoting arm, with one valve element on either side of the pivot. Any adjustment made to one of valves in an attempt to increase its operating pressure would cause the other valve to be lifted off its seat, regardless of how the adjustment was attempted. The pivot point on the arm was not symmetrically between the valves, so any tightening of the spring would cause one of the valves to lift. Only by removing and disassembling the entire valve assembly could its operating pressure be adjusted, making impromptu "tying down" of the valve by locomotive crews in search of more power impossible. The pivoting arm was commonly extended into a handle shape and fed back into the locomotive cab, allowing crews to "rock" both valves off their seats to confirm they were set and operating correctly.

Safety valves also evolved to protect equipment such as pressure vessels (fired or not) and heat exchangers. The term safety valve should be limited to compressible fluid applications (gas, vapour, or steam).

For liquid-packed vessels, thermal relief valves are generally characterized by the relatively small size of the valve necessary to provide protection from excess pressure caused by thermal expansion. In this case a small valve is adequate because most liquids are nearly incompressible, and so a relatively small amount of fluid discharged through the relief valve will produce a substantial reduction in pressure.

Flow protection is characterized by safety valves that are considerably larger than those mounted for thermal protection. They are generally sized for use in situations where significant quantities of gas or high volumes of liquid must be quickly discharged in order to protect the integrity of the vessel or pipeline. This protection can alternatively be achieved by installing a high integrity pressure protection system (HIPPS).

In the petroleum refining, petrochemical, chemical manufacturing, natural gas processing, power generation, food, drinks, cosmetics and pharmaceuticals industries, the term safety valve is associated with the terms pressure relief valve (PRV), pressure safety valve (PSV) and relief valve.

The generic term is Pressure relief valve (PRV) or pressure safety valve (PSV). PRVs and PSVs are not the same thing, despite what many people think; the difference is that PSVs have a manual lever to open the valve in case of emergency.

Relief valve (RV): an automatic system that is actuated by the static pressure in a liquid-filled vessel. It specifically opens proportionally with increasing pressure

Pilot-operated safety relief valve (POSRV): an automatic system that relieves on remote command from a pilot, to which the static pressure (from equipment to protect) is connected

Low pressure safety valve (LPSV): an automatic system that relieves static pressure on a gas. Used when the difference between the vessel pressure and the ambient atmospheric pressure is small.

Vacuum pressure safety valve (VPSV): an automatic system that relieves static pressure on a gas. Used when the pressure difference between the vessel pressure and the ambient pressure is small, negative and near to atmospheric pressure.

Low and vacuum pressure safety valve (LVPSV): an automatic system that relieves static pressure on a gas. Used when the pressure difference is small, negative or positive and near to atmospheric pressure.

In most countries, industries are legally required to protect pressure vessels and other equipment by using relief valves. Also, in most countries, equipment design codes such as those provided by the ASME, API and other organizations like ISO (ISO 4126) must be complied with. These codes include design standards for relief valves and schedules for periodic inspection and testing after valves have been removed by the company engineer.

Today, the food, drinks, cosmetics, pharmaceuticals and fine chemicals industries call for hygienic safety valves, fully drainable and Cleanable-In-Place. Most are made of stainless steel; the hygienic norms are mainly 3A in the USA and EHEDG in Europe.

The first safety valve was invented by Denis Papin for his steam digester, an early pressure cooker rather than an engine.steelyard" lever a smaller weight was required, also the pressure could easily be regulated by sliding the same weight back and forth along the lever arm. Papin retained the same design for his 1707 steam pump.Greenwich in 1803, one of Trevithick"s high-pressure stationary engines exploded when the boy trained to operate the engine left it to catch eels in the river, without first releasing the safety valve from its working load.

Although the lever safety valve was convenient, it was too sensitive to the motion of a steam locomotive. Early steam locomotives therefore used a simpler arrangement of weights stacked directly upon the valve. This required a smaller valve area, so as to keep the weight manageable, which sometimes proved inadequate to vent the pressure of an unattended boiler, leading to explosions. An even greater hazard was the ease with which such a valve could be tied down, so as to increase the pressure and thus power of the engine, at further risk of explosion.

Although deadweight safety valves had a short lifetime on steam locomotives, they remained in use on stationary boilers for as long as steam power remained.

Weighted valves were sensitive to bouncing from the rough riding of early locomotives. One solution was to use a lightweight spring rather than a weight. This was the invention of Timothy Hackworth on his leaf springs.

These direct-acting spring valves could be adjusted by tightening the nuts retaining the spring. To avoid tampering, they were often shrouded in tall brass casings which also vented the steam away from the locomotive crew.

The Salter coil spring spring balance for weighing, was first made in Britain by around 1770.spring steels to make a powerful but compact spring in one piece. Once again by using the lever mechanism, such a spring balance could be applied to the considerable force of a boiler safety valve.

The spring balance valve also acted as a pressure gauge. This was useful as previous pressure gauges were unwieldy mercury manometers and the Bourdon gauge had yet to be invented.

Paired valves were often adjusted to slightly different pressures too, a small valve as a control measure and the lockable valve made larger and permanently set to a higher pressure, as a safeguard.Sinclair for the Eastern Counties Railway in 1859, had the valve spring with pressure scale behind the dome, facing the cab, and the locked valve ahead of the dome, out of reach of interference.

In 1855, John Ramsbottom, later locomotive superintendent of the LNWR, described a new form of safety valve intended to improve reliability and especially to be tamper-resistant. A pair of plug valves were used, held down by a common spring-loaded lever between them with a single central spring. This lever was characteristically extended rearwards, often reaching into the cab on early locomotives. Rather than discouraging the use of the spring lever by the fireman, Ramsbottom"s valve encouraged this. Rocking the lever freed up the valves alternately and checked that neither was sticking in its seat.

A drawback to the Ramsbottom type was its complexity. Poor maintenance or mis-assembly of the linkage between the spring and the valves could lead to a valve that no longer opened correctly under pressure. The valves could be held against their seats and fail to open or, even worse, to allow the valve to open but insufficiently to vent steam at an adequate rate and so not being an obvious and noticeable fault.Rhymney Railway, even though the boiler was almost new, at only eight months old.

Naylor valves were introduced around 1866. A bellcrank arrangement reduced the strain (percentage extension) of the spring, thus maintaining a more constant force.L&Y & NER.

All of the preceding safety valve designs opened gradually and had a tendency to leak a "feather" of steam as they approached "blowing-off", even though this was below the pressure. When they opened they also did so partially at first and didn"t vent steam quickly until the boiler was well over pressure.

The quick-opening "pop" valve was a solution to this. Their construction was simple: the existing circular plug valve was changed to an inverted "top hat" shape, with an enlarged upper diameter. They fitted into a stepped seat of two matching diameters. When closed, the steam pressure acted only on the crown of the top hat, and was balanced by the spring force. Once the valve opened a little, steam could pass the lower seat and began to act on the larger brim. This greater area overwhelmed the spring force and the valve flew completely open with a "pop". Escaping steam on this larger diameter also held the valve open until pressure had dropped below that at which it originally opened, providing hysteresis.

These valves coincided with a change in firing behaviour. Rather than demonstrating their virility by always showing a feather at the valve, firemen now tried to avoid noisy blowing off, especially around stations or under the large roof of a major station. This was mostly at the behest of stationmasters, but firemen also realised that any blowing off through a pop valve wasted several pounds of boiler pressure; estimated at 20 psi lost and 16 lbs or more of shovelled coal.

Pop valves derived from Adams"s patent design of 1873, with an extended lip. R. L. Ross"s valves were patented in 1902 and 1904. They were more popular in America at first, but widespread from the 1920s on.

Although showy polished brass covers over safety valves had been a feature of steam locomotives since Stephenson"s day, the only railway to maintain this tradition into the era of pop valves was the GWR, with their distinctive tapered brass safety valve bonnets and copper-capped chimneys.

Developments in high-pressure water-tube boilers for marine use placed more demands on safety valves. Valves of greater capacity were required, to vent safely the high steam-generating capacity of these large boilers.Naylor valve) became more critical.distilled feedwater and also a scouring of the valve seats, leading to wear.

High-lift safety valves are direct-loaded spring types, although the spring does not bear directly on the valve, but on a guide-rod valve stem. The valve is beneath the base of the stem, the spring rests on a flange some height above this. The increased space between the valve itself and the spring seat allows the valve to lift higher, further clear of the seat. This gives a steam flow through the valve equivalent to a valve one and a half or twice as large (depending on detail design).

The Cockburn Improved High Lift design has similar features to the Ross pop type. The exhaust steam is partially trapped on its way out and acts on the base of the spring seat, increasing the lift force on the valve and holding the valve further open.

To optimise the flow through a given diameter of valve, the full-bore design is used. This has a servo action, where steam through a narrow control passage is allowed through if it passes a small control valve. This steam is then not exhausted, but is passed to a piston that is used to open the main valve.

There are safety valves known as PSV"s and can be connected to pressure gauges (usually with a 1/2" BSP fitting). These allow a resistance of pressure to be applied to limit the pressure forced on the gauge tube, resulting in prevention of over pressurisation. the matter that has been injected into the gauge, if over pressurised, will be diverted through a pipe in the safety valve, and shall be driven away from the gauge.

There is a wide range of safety valves having many different applications and performance criteria in different areas. In addition, national standards are set for many kinds of safety valves.

Safety valves are required on water heaters, where they prevent disaster in certain configurations in the event that a thermostat should fail. Such a valve is sometimes referred to as a "T&P valve" (Temperature and Pressure valve). There are still occasional, spectacular failures of older water heaters that lack this equipment. Houses can be leveled by the force of the blast.

Pressure cookers usually have two safety valves to prevent explosions. On older designs, one is a nozzle upon which a weight sits. The other is a sealed rubber grommet which is ejected in a controlled explosion if the first valve gets blocked. On newer generation pressure cookers, if the steam vent gets blocked, a safety spring will eject excess pressure and if that fails, the gasket will expand and release excess pressure downwards between the lid and the pan. Also, newer generation pressure cookers have a safety interlock which locks the lid when internal pressure exceeds atmospheric pressure, to prevent accidents from a sudden release of very hot steam, food and liquid, which would happen if the lid were to be removed when the pan is still slightly pressurised inside (however, the lid will be very hard or impossible to open when the pot is still pressurised).

"Trial of HMS Rattler and Alecto". April 1845. The very lowest pressure exhibited "when the screw was out of the water" (as the opponents of the principle term it) was 34 lb, ranging up to 60 lb., on Salter"s balance.

There is a wide range of safety valves available to meet the many different applications and performance criteria demanded by different industries. Furthermore, national standards define many varying types of safety valve.

The ASME standard I and ASME standard VIII for boiler and pressure vessel applications and the ASME/ANSI PTC 25.3 standard for safety valves and relief valves provide the following definition. These standards set performance characteristics as well as defining the different types of safety valves that are used:

ASME I valve - A safety relief valve conforming to the requirements of Section I of the ASME pressure vessel code for boiler applications which will open within 3% overpressure and close within 4%. It will usually feature two blowdown rings, and is identified by a National Board ‘V’ stamp.

ASME VIII valve- A safety relief valve conforming to the requirements of Section VIII of the ASME pressure vessel code for pressure vessel applications which will open within 10% overpressure and close within 7%. Identified by a National Board ‘UV’ stamp.

Full bore safety valve - A safety valve having no protrusions in the bore, and wherein the valve lifts to an extent sufficient for the minimum area at any section, at or below the seat, to become the controlling orifice.

Conventional safety relief valve -The spring housing is vented to the discharge side, hence operational characteristics are directly affected by changes in the backpressure to the valve.

Balanced safety relief valve -A balanced valve incorporates a means of minimising the effect of backpressure on the operational characteristics of the valve.

Pilot operated pressure relief valve -The major relieving device is combined with, and is controlled by, a self-actuated auxiliary pressure relief device.

Power-actuated safety relief valve - A pressure relief valve in which the major pressure relieving device is combined with, and controlled by, a device requiring an external source of energy.

Standard safety valve - A valve which, following opening, reaches the degree of lift necessary for the mass flowrate to be discharged within a pressure rise of not more than 10%. (The valve is characterised by a pop type action and is sometimes known as high lift).

Full lift (Vollhub) safety valve -A safety valve which, after commencement of lift, opens rapidly within a 5% pressure rise up to the full lift as limited by the design. The amount of lift up to the rapid opening (proportional range) shall not be more than 20%.

Direct loaded safety valve -A safety valve in which the opening force underneath the valve disc is opposed by a closing force such as a spring or a weight.

Proportional safety valve - A safety valve which opens more or less steadily in relation to the increase in pressure. Sudden opening within a 10% lift range will not occur without pressure increase. Following opening within a pressure of not more than 10%, these safety valves achieve the lift necessary for the mass flow to be discharged.

Diaphragm safety valve -A direct loaded safety valve wherein linear moving and rotating elements and springs are protected against the effects of the fluid by a diaphragm

Bellows safety valve - A direct loaded safety valve wherein sliding and (partially or fully) rotating elements and springs are protected against the effects of the fluids by a bellows. The bellows may be of such a design that it compensates for influences of backpressure.

Controlled safety valve - Consists of a main valve and a control device. It also includes direct acting safety valves with supplementary loading in which, until the set pressure is reached, an additional force increases the closing force.

Safety valve - A safety valve which automatically, without the assistance of any energy other than that of the fluid concerned, discharges a quantity of the fluid so as to prevent a predetermined safe pressure being exceeded, and which is designed to re-close and prevent further flow of fluid after normal pressure conditions of service have been restored. Note; the valve can be characterised either by pop action (rapid opening) or by opening in proportion (not necessarily linear) to the increase in pressure over the set pressure.

Direct loaded safety valve -A safety valve in which the loading due to the fluid pressure underneath the valve disc is opposed only by a direct mechanical loading device such as a weight, lever and weight, or a spring.

Assisted safety valve -A safety valve which by means of a powered assistance mechanism, may additionally be lifted at a pressure lower than the set pressure and will, even in the event of a failure of the assistance mechanism, comply with all the requirements for safety valves given in the standard.

Supplementary loaded safety valve - A safety valve that has, until the pressure at the inlet to the safety valve reaches the set pressure, an additional force, which increases the sealing force.

Note; this additional force (supplementary load), which may be provided by means of an extraneous power source, is reliably released when the pressure at the inlet of the safety valve reaches the set pressure. The amount of supplementary loading is so arranged that if such supplementary loading is not released, the safety valve will attain its certified discharge capacity at a pressure not greater than 1.1 times the maximum allowable pressure of the equipment to be protected.

Pilot operated safety valve -A safety valve, the operation of which is initiated and controlled by the fluid discharged from a pilot valve, which is itself, a direct loaded safety valve subject to the requirement of the standard.

The common characteristic shared between the definitions of conventional safety valves in the different standards, is that their operational characteristics are affected by any backpressure in the discharge system. It is important to note that the total backpressure is generated from two components; superimposed backpressure and the built-up backpressure:

Subsequently, in a conventional safety valve, only the superimposed backpressure will affect the opening characteristic and set value, but the combined backpressure will alter the blowdown characteristic and re-seat value.

The ASME/ANSI standard makes the further classification that conventional valves have a spring housing that is vented to the discharge side of the valve. If the spring housing is vented to the atmosphere, any superimposed backpressure will still affect the operational characteristics. Thiscan be seen from Figure 9.2.1, which shows schematic diagrams of valves whose spring housings are vented to the discharge side of the valve and to the atmosphere.

By considering the forces acting on the disc (with area AD), it can be seen that the required opening force (equivalent to the product of inlet pressure (PV) and the nozzle area (AN)) is the sum of the spring force (FS) and the force due to the backpressure (PB) acting on the top and bottom of the disc. In the case of a spring housing vented to the discharge side of the valve (an ASME conventional safety relief valve, see Figure 9.2.1 (a)), the required opening force is:

In both cases, if a significant superimposed backpressure exists, its effects on the set pressure need to be considered when designing a safety valve system.

Once the valve starts to open, the effects of built-up backpressure also have to be taken into account. For a conventional safety valve with the spring housing vented to the discharge side of the valve, see Figure 9.2.1 (a), the effect of built-up backpressure can be determined by considering Equation 9.2.1 and by noting that once the valve starts to open, the inlet pressure is the sum of the set pressure, PS, and the overpressure, PO.

In both cases, if a significant superimposed backpressure exists, its effects on the set pressure need to be considered when designing a safety valve system.

Once the valve starts to open, the effects of built-up backpressure also have to be taken into account. For a conventional safety valve with the spring housing vented to the discharge side of the valve, see Figure 9.2.1 (a), the effect of built-up backpressure can be determined by considering Equation 9.2.1 and by noting that once the valve starts to open, the inlet pressure is the sum of the set pressure, PS, and the overpressure, PO.

Balanced safety valves are those that incorporate a means of eliminating the effects of backpressure. There are two basic designs that can be used to achieve this:

Although there are several variations of the piston valve, they generally consist of a piston type disc whose movement is constrained by a vented guide. The area of the top face of the piston, AP, and the nozzle seat area, AN, are designed to be equal. This means that the effective area of both the top and bottom surfaces of the disc exposed to the backpressure are equal, and therefore any additional forces are balanced. In addition, the spring bonnet is vented such that the top face of the piston is subjected to atmospheric pressure, as shown in Figure 9.2.2.

The bellows arrangement prevents backpressure acting on the upper side of the disc within the area of the bellows. The disc area extending beyond the bellows and the opposing disc area are equal, and so the forces acting on the disc are balanced, and the backpressure has little effect on the valve opening pressure.

Bellows failure is an important concern when using a bellows balanced safety valve, as this may affect the set pressure and capacity of the valve. It is important, therefore, that there is some mechanism for detecting any uncharacteristic fluid flow through the bellows vents. In addition, some bellows balanced safety valves include an auxiliary piston that is used to overcome the effects of backpressure in the case of bellows failure. This type of safety valve is usually only used on critical applications in the oil and petrochemical industries.

Since balanced pressure relief valves are typically more expensive than their unbalanced counterparts, they are commonly only used where high pressure manifolds are unavoidable, or in critical applications where a very precise set pressure or blowdown is required.

This type of safety valve uses the flowing medium itself, through a pilot valve, to apply the closing force on the safety valve disc. The pilot valve is itself a small safety valve.

The diaphragm type is typically only available for low pressure applications and it produces a proportional type action, characteristic of relief valves used in liquid systems. They are therefore of little use in steam systems, consequently, they will not be considered in this text.

The piston type valve consists of a main valve, which uses a piston shaped closing device (or obturator), and an external pilot valve. Figure 9.2.4 shows a diagram of a typical piston type, pilot operated safety valve.

The piston and seating arrangement incorporated in the main valve is designed so that the bottom area of the piston, exposed to the inlet fluid, is less than the area of the top of the piston. As both ends of the piston are exposed to the fluid at the same pressure, this means that under normal system operating conditions, the closing force, resulting from the larger top area, is greater than the inlet force. The resultant downward force therefore holds the piston firmly on its seat.

If the inlet pressure were to rise, the net closing force on the piston also increases, ensuring that a tight shut-off is continually maintained. However, when the inlet pressure reaches the set pressure, the pilot valve will pop open to release the fluid pressure above the piston. With much less fluid pressure acting on the upper surface of the piston, the inlet pressure generates a net upwards force and the piston will leave its seat. This causes the main valve to pop open, allowing the process fluid to be discharged.

When the inlet pressure has been sufficiently reduced, the pilot valve will reclose, preventing the further release of fluid from the top of the piston, thereby re-establishing the net downward force, and causing the piston to reseat.

Pilot operated safety valves offer good overpressure and blowdown performance (a blowdown of 2% is attainable). For this reason, they are used where a narrow margin is required between the set pressure and the system operating pressure. Pilot operated valves are also available in much larger sizes, making them the preferred type of safety valve for larger capacities.

One of the main concerns with pilot operated safety valves is that the small bore, pilot connecting pipes are susceptible to blockage by foreign matter, or due to the collection of condensate in these pipes. This can lead to the failure of the valve, either in the open or closed position, depending on where the blockage occurs.

The terms full lift, high lift and low lift refer to the amount of travel the disc undergoes as it moves from its closed position to the position required to produce the certified discharge capacity, and how this affects the discharge capacity of the valve.

A full lift safety valve is one in which the disc lifts sufficiently, so that the curtain area no longer influences the discharge area. The discharge area, and therefore the capacity of the valve are subsequently determined by the bore area. This occurs when the disc lifts a distance of at least a quarter of the bore diameter. A full lift conventional safety valve is often the best choice for general steam applications.

The disc of a high lift safety valve lifts a distance of at least 1/12th of the bore diameter. This means that the curtain area, and ultimately the position of the disc, determines the discharge area. The discharge capacities of high lift valves tend to be significantly lower than those of full lift valves, and for a given discharge capacity, it is usually possible to select a full lift valve that has a nominal size several times smaller than a corresponding high lift valve, which usually incurs cost advantages.Furthermore, high lift valves tend to be used on compressible fluids where their action is more proportional.

In low lift valves, the disc only lifts a distance of 1/24th of the bore diameter. The discharge area is determined entirely by the position of the disc, and since the disc only lifts a small amount, the capacities tend to be much lower than those of full or high lift valves.

Except when safety valves are discharging, the only parts that are wetted by the process fluid are the inlet tract (nozzle) and the disc. Since safety valves operate infrequently under normal conditions, all other components can be manufactured from standard materials for most applications. There are however several exceptions, in which case, special materials have to be used, these include:

Cast steel -Commonly used on higher pressure valves (up to 40 bar g). Process type valves are usually made from a cast steel body with an austenitic full nozzle type construction.

For all safety valves, it is important that moving parts, particularly the spindle and guides are made from materials that will not easily degrade or corrode. As seats and discs are constantly in contact with the process fluid, they must be able to resist the effects of erosion and corrosion.

The spring is a critical element of the safety valve and must provide reliable performance within the required parameters. Standard safety valves will typically use carbon steel for moderate temperatures. Tungsten steel is used for higher temperature, non-corrosive applications, and stainless steel is used for corrosive or clean steam duty. For sour gas and high temperature applications, often special materials such as monel, hastelloy and ‘inconel’ are used.

Standard safety valves are generally fitted with an easing lever, which enables the valve to be lifted manually in order to ensure that it is operational at pressures in excess of 75% of set pressure. This is usually done as part of routine safety checks, or during maintenance to prevent seizing. The fitting of a lever is usually a requirement of national standards and insurance companies for steam and hot water applications. For example, the ASME Boiler and Pressure Vessel Code states that pressure relief valves must be fitted with a lever if they are to be used on air, water over 60°C, and steam.

A test gag (Figure 9.2.7) may be used to prevent the valve from opening at the set pressure during hydraulic testing when commissioning a system. Once tested, the gag screw is removed and replaced with a short blanking plug before the valve is placed in service.

The amount of fluid depends on the particular design of safety valve. If emission of this fluid into the atmosphere is acceptable, the spring housing may be vented to the atmosphere – an open bonnet. This is usually advantageous when the safety valve is used on high temperature fluids or for boiler applications as, otherwise, high temperatures can relax the spring, altering the set pressure of the valve. However, using an open bonnet exposes the valve spring and internals to environmental conditions, which can lead to damage and corrosion of the spring.

When the fluid must be completely contained by the safety valve (and the discharge system), it is necessary to use a closed bonnet, which is not vented to the atmosphere. This type of spring enclosure is almost universally used for small screwed valves and, it is becoming increasingly common on many valve ranges since, particularly on steam, discharge of the fluid could be hazardous to personnel.

Some safety valves, most commonly those used for water applications, incorporate a flexible diaphragm or bellows to isolate the safety valve spring and upper chamber from the process fluid, (see Figure 9.2.9).

There are lots of industrial valves in general industry, power plant, chemical plant, refining, oil and gas, water and wastewater treatment, with a variety of valve types, functions, size, materials, pressure rating, operation method, etc., It’s confusing for purchaser or Newbies who have just entered the valve industry.

So before introducing much terminology and technical knowledge, I shall picture a simple diagram to get a more intuitive understanding of all valves for you.

The ball valve is a type of isolation valve which is the most common valve used in industry, because of its excellent operating characteristics. The ball valve can be contacted by welding, threaded and flanged, and available in a wide range of sizes, materials, temperature, pressure, and tight shutoff.

Our headquarters STONE Valve in Taiwan has over 30 years of experience in manufacturing ball valves. Your project of the ball valve will take a professional quote and technical support.

Gate valve is the most common isolation valve in industry, with a linear motion to open and close the flow. As its disc is like a gate, so named a gate valve. There are various types of gate valves, knife gate valves, wedge gate valves, parallel slide gate valves, pipeline slab gate valves, and so on.

Gate valve only works for fully close and fully open, it can not be used for proportion controlling conditions. But as the passageway of a gate valve is unobstructed, which results in minimum pressure loss.

● Action time: Compare with the ball valve, the gate valve needs more time to open to close the valve. So it is usually used for application which doesn’t need frequent opening and closing, just simply to isolate the pipeline.

● Sealing: Ball valve has more excellent sealing performance than the gate valve. In the fully closed position and with flow pressure, the gate valve has a positive seal, but under very low pressure like 3psig, it maybe has a little leakage out of the gate valve seat.

Globe valve, here I talk about the conventional globe valve, not globe type control valve. I put a globe type control valve to the control valve part, which here means a stop valve.

A globe valve is often used for isolation service, the flow path through the globe valve follows a constantly changing process, which increased flow resistance, that’s why the globe valve has a higher pressure drop than the gate valve, plug valve, and ball valve(those valves are straight-through path)

According to the different body designs, the globe valve is classified as a Tee pattern globe valve, Z type globe valve, Y pattern globe valve, and angle pattern globe valve.

As a general rule, you can check the height of the screw stem between the handwheel and yoke, if only 1 – 3 thread displacement that means the globe valve is in a close position. When the valve is at an open position, it will show more height of the thread.

As a general rule, turn the handwheel clockwiseto close the globe valve, and turn counterclockwise to open the valve. There will be a switch mark and arrow on the handwheel.

The lifting check valve usually includes a piston check valve and ball check valve, it is particularly suitable for high-pressure conditions and special installation positions. The lifting check valve can be installed vertical pipeline or horizontal position.

The check valve also called the non-return valve which only allows water, air, steam, or other medium flow one-way direction. The main function of the check valve includes 4 points. To protect the pump or expensive equipment from reverse flow damage.

In a general rule, for the steam system here are 2 typical ways to use a check valve. If the outlet of the trap is recycled into the same condensate collection line, it needs to install a check valve, in case to prevent condensate water discharged from equipment in operation may flow back to other equipment that is not running.

There are many reasons to cause a water hammer in steam pipe systems. One of the main causes of water hammer in the condensate recovery line is because of the backflow of condensate from the lifting pipeline. The installation of check valves in these places is of great help in preventing water hammers caused by backflow.

As a general rule, the high pressure at the outlet of the pump can be directly sent to the boiler, the pipeline connected with the high-pressure main pipe, or to the high-level water tank. During operation, when the pump suddenly stops running for some reason, the pressure in the pump disappears, and the high-pressure water connected to the outlet of the pump will flow back to the pump in the reverse direction. So here need to install a check valve(outlet of the pump), it will be closed immediately when happened this situation, to prevent high-pressure water from flowing back to the pump. If the outlet of the pump is not equipped with a check valve, the high-pressure water will flow back to the pump in the reverse direction, and the impeller of the pump will reverse under the impact of the high-pressure water. The impeller or the other parts will be damaged because of the impact load of high-pressure water on it, also the main pipe pressure decrease, and the boiler water level will drop, which will affect the safe operation.

Check valve plays a very important role in the industry system, it may not the most expensive valve but is like a guard to prevent expensive device effects due to backflow damage.

Here are the top 4 reasons that may cause check valve failure. Incorrect selection and installationThere are many types of check valves, and selecting the right type, and size for the system is crucial. So make sure the check valve is meet your application, especially for flow capacity data. Then please note the flow direction of the check valve and the position and direction of the check valve during installation.

Routine maintenance work is very necessary for industrial processes. Check carefully during the maintenance procedure, for the ball valve, gate valve, and globe valve, check valve those general valves, lookout for signs of the bonnet, body, and actuator(if assembly), and also check the pipeline if there has metal impurity, which will cause damage of valve seat or internal components, even cause valve stuck and can’t work well. If you find out any signs of wear, replace damaged components or complete valves as soon as possible.

Except for the wrong selection of check valves, most check valves fail because of a swing pin or spring broken. It will cause the check valve absolutely fail to work or can’t shut off tightness or fast response.

If the check valve work at high-temperature application, you should observe these valves often, in case to prevent the valve fails early due to high temperature. If you see any sign of wear on the check valve, replace them immediately to avoid more loss.

So check valve can’t reduce water pressure, more important is it can’t discharge fluids from low pressure into a higher pressure line, because the back pressure is higher than the upstream pressure/inlet pressure of the check valve, and the swing or disc can’t open.

The silent check valve is a priority design of silent operation with positively closing, and prevents water hammer, surges and vibration. The silent check valve combine of body, seat, disc, spring, sleeve, o-ring and retaining screws, etc., Body 2. Retaining 3. Disc 4. Spring 5. Sleeve 6. O-ring

A regular check valve can’t stop a water hammer, but because of a slam shut off, or a sudden valve closure, only a non-slam check valve, nozzle check valve or silent check valve can prevent a water hammer.

A spring-loaded check valve is one common kind of non-return valve, which allows flow in one direction, in case prevent fluids backflow. Usually, a spring-loaded check valve is suitable for reducing water hammer, and benefit can be installed in any position, no matter horizontal, vertical, or otherwise.

The swing check valve and spring-loaded check valve are both used to prevent reverse flow. Many people ask which is better, a swing check valve or a spring-loaded check valve?

A responsible engineer will not simply answer which is better, but explain how to select the right type of check valve for your application. Here we just list some cases. A swing check valve only installation of horizontal flows or vertical upward flows. But the spring-loaded check valve can be installed in any position.

A check valve is just a simple non-return valve, but a backflow preventer is a module assembly of check valves. It is used in high-hazard environments and needs to completely protect the flow safe while even one part failed.

A butterfly valve is a 90° turn rotational motion valve that is used to on/off or control the flowing medium in a process. And particularly for large capacity conditions.

As a general rule, a butterfly valve is a bi-direction industrial valve, but it does have a preferred flow direction in case to protect the valve and extends service life, also with lower operating torque.

The ball valve and butterfly valve both can isolate fluids in the processing system. So what is the exact difference between the ball valve and butterfly valve? We are going to describe the difference from 6 points. Flow capacity.A butterfly valve can provide a larger flow capacity than a ball valve, it is easy to available in a large pipeline.

Butterfly valves are easy to clean, so they are commonly used in sewage, beer, and soda production, etc. Butterfly valves are very popular in waste treatment plants, and chemical, agricultural, and food industries.

Ball valves can be used at high temperatures or both liquid and gas with some solid particles. They are common in power plants, oil and gas, refining, and so on.

The ball valve can be used for higher temperature and pressure than the butterfly valve. Usually, below 5.0Mpa and temperature below 250 degrees C can use a butterfly valve, higher than data we can use a ball valve.

Ball valve and butterfly valve both can isolation process medium, but also can proportional flow control. But for small sizes, like below DN100, V port or segmented ball valve has better regulating performance than butterfly valve. For large sizes, we can use high performance or triple offset butterfly valves to control the flow capacity.

A plug valve is an isolation valve that is a quarter-turn shutoff valve. The plug can be designed in tapered or cylindrical form. Plug valves are available in different port types.

The lubricated plug valve has grease fitting which injects lubricant to plug face and body seat, in case to reduce friction and sealing ports. Through a radial hole, the lubrication is constantly into lubricant grooves on the plug surface.

Expanding plug valve is a special design in which the plug is made of multiple components allowing it to mechanically expand through a wedging action onto the cylindrical body.

Eccentric plug valves are basically plug valve with a plug cut in half, it has minimal friction from open to close, without a significant operating torque but shutoff performance is improved.

THINKTANK manufactures plug valves for over 10 brands with high quality and reasonable prices. Your project of the ball valve will take a professional quote and technical support.

The plug valve has a tapered or cylindrical form as a plugin for the valve body and is usually secured by a spring-loaded screw on the bottom side of the valve, or a bonnet and packing at the top end.

Difference 2 Ball valve with PTFE, RPTFE, TEFLON, Metal seat ring, and packing box. When the ball valve closes the ball, the fluids get into the dead spaces, in the open position, aggressive fluids harmes the ball surface.

A plug valve is a plug top mounted into the valve body which is equivalent to a top-mounted ball valve. Compared with a two-piece or three-piece ball valve, it is a completely different type and application product.

Advantages Of Plug Valves The valve body of the plug valve adopts an integrated top installation design, simple structure, convenient in-site maintenance, and tight shutoff with zero leakage.

Used in chemical medium(corrosive medium). In a chemical environment, the valve body is often corroded by the medium. The plug valve has strong impermeability and it can be inner lining to anti-corrosive very well.

The plug valve can be designed and produced with specific functions according to user needs. Three-way, four-way, five-way, six-way, double-valve, or multi-valve groups can be customized, as well as various jacket requirements.

The coated sleeve has surface sealing performance, which can strictly refer to the “zero leakage” test requirements of the API598 soft seal seat and can meet the requirement of ISO15848 valve stem sealing.

The general characteristics of plug valves are long service life and high reliability. It is suitable for a variety of corrosive, abrasive, toxic, continuous operations and other media and equipment, and has the advantages of application in the chemical industry.

Disadvantages Of Plug Valve The surface seal design increases the requirements for driving torque. For pneumatic actuators, the requested torque is larger than ball valves, and it will increase the user’s costs.

For example, in the PP process, the main shut-off valve uses a plug valve instead of a ball valve, and the high-frequency switch valve uses a ball valve, so the pneumatic plug valve is basically used in the main cut-off position.

The price of plug valves is higher than ball valves. However, as the reliability of the plug valve and the total life cycle cost are gradually accepted by domestic users, more and more users will need a plug valve that continues to use the original process design.

The safety valve is a special valve that can protect equipment from damaging or exploding. Commonly safety valve is installed in pressure vessels and automatically opens immediately when the accumulation of pressure in a system or vessel is beyond a preset limit.It simply allows the excess pressure to relieve, to prevent any disaster.

Safety valves are widely applied in chemical plants, power plants, boilers and gas storage tanks, petrochemicals, pharmaceuticals, and many more. It controls the pressure and discharges a certain amount of fluid by itself without any additional supply of energy. Best supplier of safety valves in China – THINKTANK valve

There are three types of safety valves in thinktank’s production line. Spring-loaded safety valveA spring-loaded safety valve adopts the force of spring press on the disc against the inlet pressure.

Pilot operated safety valvePilot-operated safety valves are a combination of pilot assembly and main valve, the reliving pressure and reseating pressure of the pilot-operated safety valve is controlled by the pilot assembly, which acts as a spring-loaded safety valve. Pilot operated safety valve used in high pressure or large size variations, it has more precise accuracy and fast response.

In general, the safety valve and relief valve are both used to release the overload pressure from a pressure vessel system. So what is the exact difference between them? From technical definitions, the safety valve does differently from the relief valve.

A safety valve refers to a pressure valve that is designed to protect life, equipment, and processes. It means the safety valve is the last resort valve that releases pressure to prevent an accident when all other relief valves have failed to adequately release pressure within a system. Simplysay the safety valve is a failsafe.

A relief valve is a pressure relief valve that is designed to help the processing facility avoid system failures, and protect equipment from overpressurized conditions. A relief valve is used to control pressure for the optimal functionality of the system.

The safety valve’s only purpose is safety, which is designed to release pressure in the system failure or emergency issue immediately. Instead of controlling the pressure of a system, the safety valve open completely and immediately to prevent a disaster.

A relief valve is a pressure relief valve(PRV), which is designed to control pressure in a system, commonly used for compressed air, water, and steam system. The opening of the relief valve is proportional to the increase in system pressure. The relief valve gradually opens, returning the system to a preset pressure level. When this pressure level is reached, the valve will close again.

For a safety valve, the opening is immediately when the system pressure reaches the set pressure, to prevent system failure, in order to protect people, property, processes, and environments. It is a safe-fail device which capable of operating at all times. The safety valve is the last resort to prevent a disaster from overpressure conditions.

For a relief valve, the opening is proportional to the increase in the vessel pressure. It means the opening of the relief valve is gradual, not immediately, it allows open only at a preset pressure and releasing fluids until the pressure drops to the desired set pressure.

A setpoint is not equal to set pressure. For a pressure relief valve, a setpoint is a certain pressure level at which PRV opened. Let me explain it, a setpoint of relief valve is set below the maximum system pressure allowed before overpressure conditions occur, it is adjusted to the lowest maximum pressure rating.

So we keep a safety valve fitted in a boiler to release exceed the pressure in case to prevent such accidents. You may ask why not use a relief valve but a safety valve, you can read the above article named What is the difference between a safety valve and a relief valve?

The function of a safety valve in a boiler is when the system pressure reaches the setpoint, it will open sharp and the opening will be full until the pressure drop to around 4~5% below the working pressure.

A simple example may be very easy to understand if the set pressure is 7 bar, then when the system pressure reaches 7 bar, the safety valve will be full opening. But for the relief valve, if set pressure at 10 bar, then at 11 bar, the relief valve will open more to release an extra 1 bar.

The nozzle inside of the safety valve starts to receive a high pressure from the inlet port, when the pressure increases higher than the predetermined pressure, the disc starts to lift and discharge the fluid. and when the inlet pressure decreases while the set pressure, the force of spring closes the disc.

THINKTANK is a well-known brand in China, focus on manufacturing control valves for over 15 years. We supply an eccentric plug control valve, single-seated control valve, double-seated control valve, three-way control valve, cage type control valve, and so on, which can be custom engineered to perform specific functions for the end-users requirements.

A control valve is one of the most important parts of the control loop. The main function is regulating pressure, temperature, flow rate, or other variables of the process medium in the industry. As a professional globe control valve manufacturer, THINKTANK provides a wide range of control valves for chemicals, oil&gas, power plants, refining plants, pharmaceuticals, etc.

The control valve is the most common final control device in the process, The control valve regulates the flow of a fluid, such as gas, steam, water, or chemical mixture, to compensate for load disturbances and make the controlled process variable as close as the desired setpoint.

There are three typical types of actuated control valves in the process, pneumatically actuated, electric actuated/motorized actuated, and hydraulic actuated. The working principles of the valve are similar, but a bit different from the actuator part with different ways to operate.

● Pneumatic actuatedUsually, the pneumatic actuator will complete with the positioner along with the assembly of the control valve. Pneumatic actuator receives the air supply from an external source and force to the diaphragm or piston of pneumatic actuator, meanwhile valve positioner receives an input signal 4-20mA or 3-15PSI or others analog signal from PID, and turns the signal response to the actuator, and finally makes actuator proportion drive the valve stem downward/upward strokes control valve.

● Hydraulic actuatedThe hydraulic actuator has more force than the pneumatic and electric actuator, and it uses hydraulic oil to drive the actuator to regulate the control valve. They are mainly used in high-safety systems such as steam turbine exhaust pipes, blast furnace gas residual pressure power generation devices (TRT), and industrial pipe networks with seawater, sewage, flue gas, air, oil, etc. as emergency shut-off valves.

A self-operated valve is not required for auxiliary energy to the active valve but uses the process medium energy itself. It means there is no need for extra pneumatic, electric, or hydraulic power to operate the valve.

A self-operated pressure-reducing valve is a mechanical device used to control upstream/inlet or downstream/outlet pressure in natural gas plants. Also, it can be used for steam, air, water, and other fluids.

A self-operated pressure-reducing valve consists of three parts, a loading component(spring), ameasuring component(diaphragm/piston self-operated actuator), and a restrictive component(valve).

The measuring component is directly connected to the process medium(natural gas) and generates a force against a loading force from the spring, then drive restricting component – valve release pressure.

For example, if a self-operated pressure reducing valve is used to controlling downstream pressure, natural gas medium, the set pressure is 1 bar. So we put the control line at the regulator outlet connected to the downstream pipeline, to measure the process pressure and respond to the diaphragm.

The process medium flows through the valve between the seat and plug by the arrow direction, the downstream pressure P2 is transmitted over the actuator chamber and the control line to the operating diaphragm where it is converted into a positioning force. Then this force act on the valve plug depending on the force of the setpoint springs.

When the downstream pressure P2 increases, the force P2 acts on the diaphragm also increases. At this time, the force on the diaphragm is greater than the force of the set spring, so the valve plug moves toward the closed position, the opening of the valve decreases, and P2 decreases until the force on the diaphragm is balanced with the spring force. So that P2 is reduced to the set value. In the same way, when the pressure P2 after the valve decreases, the action direction is opposite to the above direction

The 73X/74X Series are Habonim’s line of Flanged Full Port Ball Valvess in ANSI class 150 and ANSI class 300. Ideal for conditions which require maximum pressure drop, reducing risk of clogging with solids or slurries, Habonim’s full bore valves offer tight shutoff, long service life and durability with exceptional performance in many service applications under the most severe working conditions.

Safety valve Zaes V73 – CE Certificated as per pressure equipment directive PED 2014/68/UE and ISO 4126‐1:2004 Safety valve for overpressure relief in pressure vessels or pipe lines. Direct spring actuation system. Flanged input connection ISO and ANSI standards. Manufacturing materials as equipment or process needs (Grey cast Iron, carbon steel and acid resistant steel). It can be supplied regulated and sealed to the pressure required by the customer, with CE certificate. It includes sealing element. Cap to ensure complete watertightness and avoid manipulation. Springs adjustment range from 0.5 to 40 Bar g pressure (7‐580 Psi g).

A ball valve is a shut-off valve that allows, obstructs, and controls the flow of liquids, gases, and vapors in a piping system by rotating the ball having a bore inside the valve. The ball is mounted against two seats and has a shaft that connects it to the operating and control mechanism that rotates the ball. When the cross-section of the bore is perpendicular to the area of the flow, the fluid is not permitted to pass through the valve. The fluid flows through from the valve, and the fluid flow rate depends on the area of the bore exposed to the floor.

Ball valves are a type of quarter-turn valve along with plug valves and butterfly valves. They can be operated manually or by using an actuator. The simplest operation of a ball valve is through the use of a wrench or a lever manually turned by an operator. Torque is applied to rotate the lever arm by 90° by either clockwise or counterclockwise to open or close the valve. If the lever arm is parallel to the pipe, it indicates that the valve is open. If the lever arm is perpendicular to the pipe, it indicates that the valve is closed.

Ball valves come in many designs and features to satisfy various industrial needs. The standards and specifications for ball valves vary depending on the industry where it is utilized.

All internal components of a ball valve are contained inside the valve housing or the body. It is made of a hard and rigid metal, thermoplastic, or thermoplastic-lined metal that protects the components of the ball valve. It also allows access to the external control mechanism that rotates the ball.

The ball is a sphere that has a hole in its center. The hole in its center is called the bore. The bore serves as the flow opening of the fluid when the cross-section of the fluid flow path and the bore is coplanar. Otherwise, the flow is throttled. A ball valve may have a solid ball or a hollow ball. A solid ball has a constant opening diameter throughout its structure, which helps the fluid to smoothly flow at a constant velocity. A hollow ball, on the other hand, has a hollow internal structure, and the space inside it allows more fluid to pass through the valve. However, the larger space creates turbulence and high velocities. A hollow ball is more lightweight and cheap compared to a solid ball.

The bonnet is an extension of the valve housing that contains and protects the shaft and its packing. It may be welded or bolted to the body. It is also made of hard metal and it covers the opening made from connecting the shaft to the external control mechanism.

The valve seats provide sealing between the ball and its body. The upstream seat is adjacent to the inlet side of the valve. The downstream seat is found on the opposite side of the upstream seat which is adjacent to the discharge side of the valve.

A one-piece ball valve has a single-piece cast body that houses the internal components of the ball valve. This eliminates the risk of leakage of the fluid from the valve. One-piece ball valves are the cheapest ball valves and always have a reduced bore. A welded one-piece ball valve is more common but cannot be dismantled for cleaning and repaired once damaged; therefore, it is only used for applications with a low possibility of particle build-up, and where sanitation is not a major concern. On the other hand, screwed one-piece ball valves can be cleaned, serviced, and repaired, but dismantling requires special tools.

Split Body Ball Valves are valves that are assembled on the sides of their balls. A split body ball valve may be a two-piece or a three-piece ball valve:

A two-piece ball valve consists of housing divided into two pieces that are fitted together. The main piece contains the ball and a connection to one end, and the other piece holds the internal components together and has a connection to the other end. Two-piece housing is the most common type among ball valves. The two parts can be dismantled for cleaning, maintenance, and inspection but it requires removal of the valve from the pipe.

A three-piece ball valve consists of the housing for the internal components of the valve which are fitted and held together by bolt connections to its two ends. The ends are threaded or welded to the main pipe.

Three-piece ball valves are used for applications that rely heavily on valves, that their maintenance activities must frequently be done. They can be cleaned and serviced easily and their seats and seals can be routinely replaced by just taking the valve body out without disturbing the two ends. Three-piece ball valves are commonly used in the food and beverage and pharmaceutical industries where sanitation is crucial to safety and product quality.

A top entry ball valve allows access to the internals of the valve by simply removing the bonnet on top of the valve. This allows in-line maintenance activities (i.e., dismantling, cleaning, inspection, and repairing the valve) without removing the ball valve from the main pipe.

The floating ball is the most common ball design in ball valves. The ball is suspended inside the valve and free to move in a lateral direction when the valve is in a closed position. It is sandwiched between two seats that support the valve and hold it in place. The ball is