hydraulic safety valve symbol manufacturer

To enable engineers to communicate and understand the circuitry associated with hydraulic systems there is an International Standard for hydraulic symbols – ISO1219/1 2006

The symbols do not identify component size or their actual position on the machine however the symbols do provide vital information relating to the configurations and flow path connections.

A tiny detail of the hydraulic check valve symbol direction is wrong, which put the hydraulic check valve manufacturer in a very difficult position, the factory is almost closed. There is a devil in the details. Whether you can grasp the devil of the hydraulic check valve symbol requires you to think every day, in addition to hydraulic check valve, hydraulic check valve, and still hydraulic check valve.

When I opened the mailbox, I saw the e-mail of Adair who we had known for 3 years. There was a habit with Adair. He purchases only one type of hydraulic valves from each one hydraulic valve manufacturer. We AAK HYDRAULIC VALVE has been his supplier for the hydraulic pressure valves. After reading the email, it was actually a proofing request for a hydraulic check valve, not a hydraulic pressure valve. It was a little abnormal. I thought he sent the wrong email.

I reminded him whether the e-mail was sent by mistake. He said bluntly that he would need 3 samples of the hydraulic check valve as soon as possible, according to the drawings in his email. Somehow, I always felt there was a problem somewhere, and I went to see the drawing of the hydraulic check valve. It is found that in the layout at the bottom of the drawing, the arrow direction on the hydraulic check valve symbol is reversed. For the hydraulic check valve symbol, the arrow direction is reversed, which is fatal. It seems that a designer is unlikely to make such a low-level mistake.

When the technical team got the drawing and started proofing, they called me. The hydraulic check valve symbol on the drawing seemed wrong. I"m glad they can also find that there is an objection to the hydraulic check valve symbol. I asked what they think of the hydraulic check valve symbol. They suggested making two sets of samples, one according to the hydraulic check valve symbol on the customer"s drawing, and the other is for the hydraulic check valve symbol we understand.

When Adair received two sets of samples, he deliberately asked why they were two sets of samples. When we pointed out the details of the hydraulic check valve symbol, Adair began to tell me the devil"s story of the hydraulic check valve symbol.

6 months ago, he sent his hydraulic valve manufacturer the drawing with this hydraulic check valve symbol, which was made by their chief designer overnight. The hydraulic valve manufacturer proofed according to this drawing. As a result, the hydraulic check valve sample was also approved at one time. The devil began to make trouble from this time. The 2,000 hydraulic check valves were produced and shipped to his customer. The customer is testing a new production line and needs to use these hydraulic check valves. After installation, there is a big problem in startup and commissioning. Because of the wrong direction, the medium returned, polluting the whole new production line, and directly causing a loss of more than 260,000 US dollars. The customer sent the loss list to his boss, who asked the hydraulic valve manufacturer to bear it.

The hydraulic valve manufacturer quickly found out the reason, but did not dare to directly tell the boss that this is the problem that the hydraulic check valve symbol on your drawings is wrongly marked. If offended the designer, there will be even no opportunity to quote in the future. Now the hydraulic valve manufacturer is in a dilemma. Bear the loss, the number is large. Not to bear the loss, they only have this only customer, Adair’s company.

Who would have thought that this hydraulic check valve symbol butterfly wings directly incited the loss of more than 260,000 US dollars across the Atlantic. When the devil comes out, it seems difficult to find a way to the best of both worlds. The only way is to keep the devil in a bottle.

AAK knows that there is a devil when looking at the hydraulic check valve symbol. If there is any problem with the hydraulic check valve symbol, please contact AAK HYDRAULIC VALVE: www.aakindustry.com

The words flow control valves broadly describe any hydraulic component capable of diminishing fluid volume downstream of itself relative to upstream. It goes without saying a flow control valve only reduces flow since the laws of nature remain unbroken. The method of varying flow varies considerably and depending on the choice of valve and its location, the effect can be substantial.

Draw the fixed orifice in one of two ways as shown in Figure 1. The first, and most common method, shows the flow path surrounded by outward facing, gentle arcs. They signify a smooth compression of the fluid, but in reality, hydraulic components are rarely honed so smoothly. The second symbol with inward facing vertices depicts the less common method of drawing a fixed orifice, although it’s the one I personally prefer.

Fixed orifices are used typically used for factory settings in pumps, manifolds and valves, but offer no user adjustability. A variable orifice provides a method to control the size of the gap between the needle and its seat, thus changing the flow rate through itself. The symbol simply adds the diagonal arrow depicting adjustability in fluid power symbols. As with most symbology, the method varying flow in the physical valve is otherwise irrelevant in regard to the symbol. Additionally, neither does the adjustable symbol guarantee that flow rate will even be adjusted if there is no upstream provision to reduce or bypass flow otherwise allocated to the valve. This is, after all, positive displacement we’re talking about, and in a system with a fixed pump, fluid must go somewhere.

Classic hydraulic theory teaches us they’re not flow control valves unless and until there is a reverse flow check valve, such as in the last example of Figure 1. The check valve blocks upward flow through this valve symbol, pressing the ball into the seat when flow exists at the bottom port. Reverse flow allows the ball to lift and bypass the check valve, although a good portion of flow will still pass through the orifice, as pressure drop through both the orifice and check valve will be exactly equal to each other. The diagonal arrow shows us this flow control valve is a variable flow rate.

Although this series is focused on symbols more than any principles of fluid power, it’s important to understand the relationship with pressure and flow. In any circuit where a restriction, orifice or flow control reduces flow, pressure increases. Also, in any circumstance where downstream pressure is high, the potential to flow through a metering device is reduced. The important term to remember is pressure drop, which is a comparison of upstream and downstream pressure through an object. Any change in flow or pressure drop can have consequence, either positive or negative, on system performance.

The four symbols covered thus far represent valves that will flow at a rate dictated by pressure drop through them, and should downstream pressure rise or fall, flow will change inversely proportional. To get around this problem, a concept called pressure compensation was created, and it uses a clever technique to encourage flow when downstream pressure increases, thereby allowing a stable flow rate regardless of load or supply pressure fluctuations.

The first symbol in Figure 2 depicts the simplified version of a pressure and temperature compensated flow control. This symbol comprises the orifice arcs, the variable arrow and reverse-flow check valve, just as with a standard flow control. However, the addition of the upward facing arrowhead tells us it is pressure compensated. I cannot tell you the etymology related to this choice of graphic, but it’s standard practice, nevertheless. More easily understood is the symbol for temperature compensation, which expresses itself as a sideways thermometer. Temperature compensation could also be called viscosity compensation because it’s just a feature that allows the valve to manage flow rate despite varying oil viscosity.

The final symbol showing a detailed representation of a pressure compensated flow control is where things get complicated, but if you stick with me, you’ll understand. The variable orifice and check valve are self-explanatory, but the compensator symbol added downstream has a lot going on. Port 1 upstream of the orifice is connected to the b-side envelope of the compensator, which shows the “T” symbols to block flow at both ports. Port 2 is connected downstream of the variable orifice and feeds its pilot line to the b-side envelope of the compensator, but this shows it as normally flowing in neutral. Port 3 of the valve simply connects the whole assembly and bypasses the fun bits and provide free flow in reverse; a true flow control.

The compensator is shown as a 2-position valve, but it’s more of an infinitely variable spool valve that meters between flowing more or flowing less. The compensator is offset by a spring that provides 90 psi of effort, additive to whatever is transmitted from port 2. When flow occurs through the valve, the compensator compares pressure at the ports 1 and 2 of the variable orifice. Pressure will always be higher at port 1, so pilot pressure forces the compensator closed until port 1 pressure matches the 90-psi spring valve. Flow through the variable orifice will always represent whatever 90-psi worth of pressure drop will achieve through itself, regardless of its setting.

If we use an example of a pump capable of 12 gpm and a 3,000-psi compensator or relief valve, the pressure at port 1 will see 3,000 psi. Let’s assume we want 10 gpm at 90-psi pressure drop, so we adjust our orifice to suit. Because the compensator is installed and wants to see a 90-psi difference between ports 1 and 2, the pressure at port 2 will close the compensator to block flow until port 2 pressure is 2,910 psi. At this point, 10 gpm will be flowing through the valve while the pump is either dumping 2 gpm over the relief valve or reducing its swashplate angle slightly.

If downstream pressure rises to 1,500 psi, pilot pressure at port 2 will increase, forcing the valve open and compensating for the downstream pressure increase. What would normally result in less flow potential over a given “Delta P,” now results in the compensator opening to reduce downstream backpressure. The compensator works like a pressure reducing valve in reverse; as pressure increases, it opens wider to allow more flow that would be normally lost to reduced pressure drop.

Pressure compensators can be added to any valve of a hydraulic circuit that controls flow rate, including proportional valves. Later in this series, I’ll talk about some advanced concepts based on pressure compensators, which are sometimes called “hydrostats.” Check back soon for the next article in this series, this time covering the symbols of hydraulic pumps.

A “high response valve,” is a relatively new term used to describe valves whose performance is variable, dynamic and powerful. Previously only servo valves running technologies such as a torque motor could be classified as high response, but with the proliferation of contemporary electronics, feedback and programming, proportional valves have closed the gap. Now some proportional valves match the performance of servo valves, but for the purpose of this discussion, I’ll call them all proportional valves.

I discussed proportional valve operators in Symbology 301 – Electrical and Electronic Symbols, which appeared in the August 2019 Fluid Power World magazine. However, only the electrical operators were discussed, leaving out any holistic explanation of a high response valve. In Symbology 302, I delve deeper to elucidate how electronic and hydraulic symbology intertwines to produce hybrid symbols reflecting the purpose of each valve. I should stipulate, electronic symbols in fluid power are not representative of electrical symbols, although anyone fluent in electronic symbology catches on quickly.

As mentioned in earlier articles in this series, there exists not only the ISO 1219 standard for drawing fluid power (and electrical) symbols but also a less relevant ANSI standard for drawing symbols. However, this does not stop individual manufacturers from drawing and detailing symbols as they see fit, either for clarity or narcissism, depending on who you ask. I’ve chosen actual catalog symbols from major manufacturers, so their depictions stray from explanations outlined by me previously. Bonus points if you can figure out who is who.

I’m starting with the symbols for proportional accessories valves – in this case, a proportional relief valve and a proportional flow control. I’ve sidestepped simple symbols because I know you’ve learned the basics by now, so you’ll see no bare-bones components made proportional by way of just a diagonal arrow. These are compound symbols using various individual symbols concomitantly performing a single hydraulic function.

In Figure 1 the proportional relief valve sits nested in the dash-dot boundary line, itself illustrating the encompassing nature of this symbol. In this case, the valve is an ISO 4401 D03 subplate mounted unit, which although nothing about the symbol tells us this, the functioning P (Pressure) and T (Tank) ports are being used while the A and B work ports are simply blocked due to obsolescence. The bottom of this valve may or may not exist with O-ring grooves for the work ports, and the optioning of them depends on the functioning of the proportional valve, which could also be constructed as a work port relief valve.

Both the P and T lines are shown with fixed orifices, a feature that protects the valve from saturation of flow. The valve is intended to operate in a pilot circuit, either by controlling system pilot pressure or as the singular control over a larger valve (like a slip-in cartridge element), so it flows very little.

Pressure energy flows directly into the left of the relief valve, where the pilot line can act upon the currently offset arrow to move it into the open flow path should upstream pressure overcome the solenoid’s active pressure setting. You’ll notice this manufacturer uses no spring in the symbol of the valve, although I assure you the spring exists in the physical part. They have simplified the operator as a simple solenoid rectangle bisected with the diagonal variable arrow. The diagonal arrow will be common to most, if not all, proportional valves, showing us that the current can be varied to adjust the position of a valve spool or poppet to achieve various ends.

The manufacturer embellishes the symbol with a 7-pin connector, which is a common connector used for proportional valves with onboard electronics. Those electronics will include an amplifier circuit to take the input power and control signal and turn it into a PWM output the valve can use. As discussed in the earlier article, the triangular amplifier symbol differs slightly in fluid power from electronic symbols by way of the dashed line, so as to not confuse it with a pneumatic pilot source. A final note on this symbol is that the manufacturer used the circular connection node at the pressure port of the relief valve, something not standard for an ISO symbol.

The next symbol is also that from a major manufacturer, and at first glance appears to have a lot going on. It looks primarily like a 2/2 directional valve, and essentially it is. I’ve colorized this one to make explanations easy, but please note my color choices do not reflect any standard. It starts with a 2-way, 2-position valve symbol which is normally closed in neutral, with both A and B work ports blocked. The highly experienced among you will have noticed the dark red pilot line starting at the A port and working around to the right side positional envelope, and if you guessed this is a slip in cartridge valve, you’d be correct. This particular valve is a spool, however, rather than the traditional DIN poppet design.

The dark red pilot line tells us this valve can pilot itself open directly with pressure at port A because fluid acts upon the bottom of the spool directly and fights against only the spring force. As always, the parallel lines above and below the two operator boxes show infinitely variable positions between the two extremes.

The symbols to the left are stacked out quite wide, with three major components affecting performance. The first in magenta is the hydraulically operated pilot valve. The dark triangle (normally colored black) facing towards the operators differs from a pneumatic pilot source which would be a hollow triangle. The hydraulic pilot is required to overcome the flow forces at port A, which would prevent a direct operated valve from shifting.

The X line feeding into the bottom of the pilot triangle is the external pilot supply line, which for this valve must be equal to or higher than the work pressure at port A. The Y line is the pilot drain, which is needed to keep the spring chamber drained to allow both the pilot and main stage valves to perform predictably. Any pressure in the spring chamber of the valve can be additive to spring force, reducing valve performance or killing it altogether.

Attached to the left of the pilot actuator is the solenoid valve that operates the pilot valve, which is one and the same component — a screw-in cartridge valve in this case. This cartridge valve is actually a pressure reducing valve. The spring symbol above the pilot actuator shares a chamber with the external pilot supply coming from X. The pilot valve will reduce pressure as required to allow the valve to open, increasing flow; full pilot pressure means the valve is closed, while exhausted pilot pressure at Y will allow the valve to open fully.

The two dark orange orifice arrows pointing inward at the directional flow arrow are because this is an orifice spool, where fluid passes through the center from A to B to exert force upon the spool as a method to measure pressure drop. The force on the spool is measured by the linear transducer, the cyan symbol defined in the earlier article.

The dark blue attachment at the left is the amplifier card containing all the onboard electronics, and with the feedback from the linear transducer (which if you remember was measuring spool position and its movement-related to pressure drop), will modify the signal at the pressure reducing valve as needed to match flow rate with the desired analog input from the PLC to the amplifier card. This valve operates on a closed-loop to provide accurate flow despite viscosity, pressure or temperature fluctuations.

In Figure 2, we’ve kicked up the symbol a bit to show various primary symbols arranged in a compound symbol representing a pilot-operated proportional valve with onboard electronics and spool position feedback. Once again, I’m using the symbol as exists in the catalog of a major manufacturer, so my top students will note the differences between this and the standards I’ve covered thus far.

The pilot valve is a 4-way, 3-position proportional solenoid valve, spring-centred with a “float” spool (P blocked with A & B to tank in neutral), which is sometimes called a motor spool. The parallel lines above and below the positional envelopes surrounded by proportional coils using diagonal arrows make it clear we’re dealing with a proportional valve.

The center condition is the basic form of a float center spool but has added to it an orifice symbol to each work port. Orifices are shown in the center condition of many proportional valves to describe the nature of the spool and body combination installed in the valve. Axially machined grooves called metering notchesare added to the valve spool so that partial flow occurs even while the spool grooves are not fully extended past the internal ports of the body.

The orifices describe the metering notches, but also how it performs just off-center. The metering notches allow will allow a more gradual increase in flow rate as the valve shifts away from neutral, making this type of valve more desirable for applications accelerating smoothly from a stop. If the flow is regulated mostly while the machine is “at speed,” then more valve overlap can be used, but there tends to be a bit of a dead zone in the lower range of the command signal.

On the far right of the pilot valve is a familiar shape, although a previously undiscussed version of a symbol: the amplifier. The same triangular amplifier symbol is used, but rather than the dashed line to differentiate from a pneumatic pilot source, this valve employs three simple lines nearly trisecting the main triangle. This manufacturer came up with their own solution to prevent confusion, but I wonder if it caused more questions than answers.

The pressure and tank ports of the pilot valve are fed and drained respectively via pilot lines, which are both the same dashed line. Older versions of this example may have used the dotted drain line connecting the tank port to the tank line, but these days the dashed line represents both while allowing their obvious function to define the difference.

The work ports exit the lower valve with pilot lines crossing and then feeding into the pilot operators on either side of the main stage spool. You’ll notice the pilot operators are “floating” outside the valve, an interesting choice outside the ISO standard of a rectangular box attached to the aand benvelopes as is used on the proportional flow control symbol in Figure 1. You’ll have noticed the pilot lines cross using the obsolete semicircular jump I described as old school way back in Symbology 101, which is an odd choice in this symbol since other crossed lines simply cross as usual. My intuition tells me they didn’t feel the pilot lines crossing with the work lines would be confused as a junction, even though the appropriate nodes are used to join lines in other parts of the symbol.

The pilot lines need to cross each other to correctly direct flow from the pilot valve to the main stage valve. When the aenvelope of the pilot starts to shift, it opens the P to B flow path, sending fluid to the aoperator of the main stage spool. The opposite path exists when the b operator sends fluid from P to A across the pilot valve to shift the b operator of the main stage valve. Speaking of the b operator – it shows a symbol I’ve never seen used previously to this example.

The closed center neutral 0position is typical, as is the a position showing P to B and A to T. The b envelope shows P flowing through an orifice to A and then A also flowing through an additional orifice to B. For any directional valve, connecting the pressure port simultaneously to both work ports creates a regeneration circuit. Regeneration is a counterintuitive function that allows a cylinder to extend rapidly but inversely proportional to a reduction in force. Usually, the symbol looks like the float spool of the pilot valve, but with P joined to A and B instead. However, I suppose this unique design was required to accurately represent the sequential metering of the two orifices.

As with most proportional valves, the main stage spool also shows the parallel lines above and below the main symbol to represent infinite variability between positions. As well, the transducer symbol perched at the top left measures the absolute position of the main stage spool to confirm the pilot signals are accurately positioning its larger spool. I would think that with proportional valve symbols using onboard electronics combined with spool position feedback, it would be helpful to draw an electrical line from the transducer to the amplifier to detail the concept of closed-loop control.

A hydraulic circuit represents all the hydraulic components in a system. This includes the arrangement of the components and the behavior of the system as a whole in a universally accepted symbolic manner. In this article we will discuss the most common hydraulic symbols as represented in ISO 1219-1:2012. Armed with knowledge of how basic hydraulic components are represented in the hydraulic circuit; one can understand a wide range of different hydraulic symbols, representing components performing similar tasks with minor modifications.

A hydraulic reservoir stores hydraulic fluid. This is a must-have component in any hydraulic system. All hydraulic reservoirs are open to the atmosphere except in the case of those used in aircraft and submarines.

A hydraulic pump converts electrical and/or mechanical energy into hydraulic energy. The lower end (suction side) of a pump is connected to the hydraulic reservoir, the upper end is connected to the remaining circuit. The dark upper triangle in these hydraulic symbols indicates fluid going out of the system and hence represents a pump.

In the case of the hydraulic motor, the dark triangle is inverted indicating that the fluid is entering into the system. A hydraulic motor converts hydraulic energy into mechanical energy.

System output is represented by an arrow at 450 – this can be adjusted, In other words, that the pump/motor can deal with variable flow rate per shaft rotation. Most industrial applications use electric motors as prime movers to rotate hydraulic pumps. The electric motor is represented by the letter M inside of a circle. The curved arrow represents the direction of shaft rotation.

A pressure relief valve is a NC (normally closed) type safety valve which operates when system pressure increases above a maximum working pressure. The normally closed position is indicated by the arrow away from the center line. The dashed line indicates that the system pressure acts against spring force for valve actuation.

A direction control valve is a vital component in a hydraulic system. It controls the actuator’s position and direction by controlling the fluid flow into the actuator. Therefore direction control valves can be designated by number of ports and number of positions and are selected based on the application.

The central position is a neutral position and various neutral positions are available depending upon the application. All ports closed will increase the system pressure to the maximum – actuating the pressure relief valve. Whereas all ports connected in the neutral position will relieve the system by diverting fluid from the pump to the tank directly.

DCV can be distinguished depending upon the type of actuation. Hand levers, mechanical systems or solenoids are used to change the valve’s position. A spring is used to return to a neutral position.

The flow control valve is used to control the flow rate as well as the speed of the actuator. The position of flow control valve will lead to varied system behavior – an arrow representing the adjustable flow control.

A pressure indictaor is used to measure hydraulic pressure at any one point. Hence it is generally connected between the hydraulic pump and direction control valve

First of all you can see the electric motor driving the fixed delivery hydraulic pump in the above circuit.  A safe pressure level is maintained using the pressure relief valve which is connected after the pump.

4/3 Direction control valve is being actuated by a solenoid control with all the ports are closed during the neutral position. In the figure, the DCV is in its 1st position and hence pressurized liquid will flow towards the right side of actuator. The left side of the actuator is connected to a reservoir meaning the actuator will move towards the left side.

The improper installation of pressure relief devices can have dire consequences, causing unnecessary safety risks, and delaying operations while they are replaced or repaired. PRVs are typically one of the last lines of defense in an upset condition. To ensure that PRVs relieve and flow properly, the ASME and the National Board certify all PRV assembly programs, testing facilities, and even technicians. When you see marks and symbols on your pressure relief devices, it means that your device is certified safe because it came from a National Board and/or ASME certified organization.

The National Board sets the industry standards for pressure relief devices and is responsible for markings and symbols on their pressure relief devices are those that:

The five symbols in the above graphic above are issued by the ASME and National Board. There are others, and you may see a few different variations from time to time. Each of them denotes a specific certification:

The National Board offers the Certificate of Authorization and the “R” symbol stamp for the repair and/or alteration of boilers, pressure vessels, and other pressure-retaining items.

The simple answer? Safety. However, there’s a bit more to safety than you might think. In order to ensure safe operation, organizations like the ASME and National Board set firm standards and require the completion of specific programs to attain certification. These programs are rigorous, and the UV Assembly Program is no exception.  It’s designed to be very stringent, as it ensures consistency in the capabilities and functionality of all components in the PRV assembly process. Ideally, a PRV should be procured from a certified assembler that is also able to test and repair the device if necessary. Unfortunately, this is a tall order that not all suppliers are able to.

Vinson Process Controls has the capabilities and credentials required to assemble, test and repair pressure relief devices. In order to better serve our customers, we earned the certifications for the UV (assembly program), VR (valve repair) and T/O (testing only) certifications from the ASME and the National Board. We take the guesswork out of PRV procuring and maintenance so that our customers can relax and reap the benefits.

As a UV-certified assembler, Vinson has invested in stocking Anderson Greenwood™ and Crosby™ relief valves for faster lead times. We have a wide range of options for our customers, including same-day service, when required.  The vast majority of Vinson’s relief valve inventory is in the portable 81P valves and pilot operated valves. Apart from the combined inventory we share with Emerson, we also have access to shared inventory across all 21 of Emerson’s Impact Partners. We are proud to say that all valves assembled in our Carrolton Valve Center have met or exceeded expected shipping dates.

In addition to faster lead times, our customers can maintain confidence that the products shipping from Vinson are of the samequality as those shipping directly from Emerson’s factory. The ASME, the National Board and Emerson audit all shops, quality control processes, techniques, and valves, before and after awarding certifications.  Vinson will continue to receive audits to ensure that we are meeting or exceeding expectations over time. Our adhesion to our quality control manual means that all valves assembled by Vinson have the same factory warranty as if they were assembled in Emerson’s production line.

As a part of the Emerson Impact Partner Network, Vinson is one of the primary points of contact for direct sales of Anderson Greenwood™ and Crosby™. We are a certified UV assembler, also offering valve repair and testing services. We can offer you quotes for both repair and replacement options.  Because of this unique status, Vinson can offer competitive pricing.

In this article, you are going to learn about different types of valve symbols used in P&ID. Many types of valves are used in process piping, and each has a different symbol. This makes the valve one of the tricky parts of reading P&ID. But with practice, you can easily remember these symbols and can read P&ID effectively.

There are two types of valve symbols — first, generic symbols, and second, a symbol with a modifier. Generic symbols will tell you that there is a valve in the line, but they will not tell you about the types of the valve. Whereas the valve symbol with modifier will tell you the type of valve used in the pipeline.

Here in the image above, you can see commonly used symbols for valves. These symbols are generic in nature — for example, the first symbol of a valve.

Now when you look at the symbol on the drawing, it just gives you an indication that some kind of valve is used, but it will not provide you with information about the type of valve, whether it is a gate, globe, or plug type valve. There are dedicated symbols for a gate, globe, plug, and ball valves which I will explain to you in minutes.

Similarly, the next two symbols are for three-way and four-way valves. It can be a plug or ball valve. The subsequent two symbols are a check valve and a stop check valve. These check valves can be swing check or lift check valves.

The next symbol is the excess flow valve. You can see that it is the same as a check valve the only difference is the written text below the valve symbol. You must be very careful while reading this type of symbol as it can easily be overlooked.

The last symbol is of automatic recirculation valve. This type of valve is used in the pump discharge line to ensure the pump will not suffer from low inlet pressure, which leads to cavitation.

Here in the image above, the first symbol is of angle valve. In most cases, a globe valve is used as an angle valve. The next symbol is the relief valve used to protect the piping system or equipment from overpressure.

Now the breather valve is used on the cone roof tank. This valve serves the function of the relief valve and vacuum valve. In the event of over-pressure, this valve release the pressure, and in case a vacuum is created in the tank, this valve allows air to enter the tank. Just like breathing air in and out.

The vacuum valve prevents damage to the equipment from negative pressure. Pilot-operated relief valves are just working as relief valves but are used for large-size piping. This type uses a small relief valve to operate the main relief valve. This arrangement is cost-effective in large-size relief operations.

In the image above, you can see the gate valve. Now see the P&ID symbol for the gate valve. It is a modification of a generic valve symbol by inserting a vertical line between two triangles. Three symbols shown below are the gate valve symbols used in isometric drawings. The first is for butt-welding ends, the second is for flanged end valve, and the third is for socket end connection.

For a globe valve, a symbol is modified by adding a small dark circle between triangles. You can see that P&ID and isometric symbols are almost the same, with the only change in end types.

You can see that there are two P&ID symbols for a ball valve. The reason is that P&ID and isometric drawing symbols are changed from company to company. So if you switch the company, you should be aware of this. Similarly, you can see the ISO symbols for butt, flanged, and socket ends ball valve.

Same as a ball valve, a needle valve also has multiple P&ID symbols. If you can see that even though these symbols are different, you can still easily interpret them. If you are using second P&ID symbols, your isometric symbol will be changed accordingly.

For the plug valve, the first symbol is a bit confusing with a globe valve. If you remember the symbol of a globe valve, it has a dark circle in between the triangle, whereas here, only the circle outline is there. So when you see this type of symbol, better to double-check the drawing.

The butterfly valve symbol is the only symbol where a full triangle is not used. If you refer to the first symbol, it is similar to a globe valve, but a triangle is not full. The alternative symbol is clearer in this case. For isometric symbols, you can see that there is no socket end butterfly valve.

Here is the diaphragm valve. There is no butt-welded diaphragm valve available. Most diaphragm valves are flange type, and they are used to handle process media with solid particles.

You can see the symbols in the image above with a special note. The first symbol is a special valve. The word NC return below the second symbol is more important. It indicates that this valve remains closed during normal operation. Now the next two symbols are also used alternatively to show the valve position during normal operation.

Hydraulic Right Angle Check Valve. | SEVEN OCEAN HYDRAULICS - A world-class manufacturer of high performance hydraulic valves, power units and accessories.

Located in Taiwan since 1989, SEVEN OCEAN HYDRAULIC INDUSTRIAL CO., LTD. has been a hydraulic valves, power units and accessories manufacturer. Their main products, include Right Angle Check Valve, Solenoid Operated Directional Control Valves, Pilot Operated Directional Control Valves, 4/2 Directional Control Valves, 4/3 Directional Control Valves, Variable Volume Vane Motor Pumps, Modular Stack Valves, Sandwich Valves, Hydraulic Power Units, Hydraulic Pressure Control Valves and Flow Control Valves, which are suitable for forklift, machine tool, plastic injection and recycling electrical machinery industries .

SEVEN OCEAN HYDRAULICS"s Right Angle Check Valve are reliable, sustainable, and cost effective, bringing you long-term value at an affordable price-point. With over 31 years of experience in manufacturing hydraulic systems, valves and components, Seven Ocean Hydraulics is able to streamline production time and has a greater control over product quality with in-house manufacturing of core components. We have gained trust from world- renowned brands for OEM projects, providing essential components for hydraulic products that are seen and used all over the world.

SEVEN OCEAN HYDRAULICS has been offering customers high-quality hydraulic valves, both with advanced technology and 31 years of experience, SEVEN OCEAN HYDRAULICS ensures each customer"s demands are met.

Hydraulic symbols provide a clear representation of the function of each hydraulic component. Laying each symbol out on the page in the same sequence the components are used in the circuit allows people to understand the complete function of the hydraulic equipment.

Poppet, one-way, shuttle, or check valves are shown as a ball sitting on a seat. Pass flow through the seat and the valve opens. Pass flow from the ball side and the valve will close.

Poppet or check valves have a physical seat that the valve presses against. This positive connection may exhibit zero, or more likely a very small leakage across it.

In many cases, these are the cheapest and most simple valves but they also have the potential to be the largest, most complicated, expensive, and difficult to control.

Most hydraulic components are controlled when pressure is applied to one side of a piston or another. In the case of cylinders, the force generated by the piston will move and drive the load. In the case of a directional valve, the force is used to move a spool which opens different passageways to allow the fluid to flow along different pipelines.

Spool valves rely on tiny clearances to allow them to move freely. These spool clearances are small enough to hold the pressure but still large enough to allow a small amount of fluid to leak past. Cylinder pistons include seals which will exhibit much smaller leakages.

An orifice is just a small hole, either fixed or adjustable. With increasing flow across an orifice there will also an increasing pressure drop across it, this pressure is commonly used to open or close other spool valves or poppets. Alternately if a system has a specific set pressure then the orifice might be used to control the flow rate along its pipework.

Squares and rectangles form the basis of pressure and directional control valves. A single box for pressure control and multiple boxes for directional control.

The valve sits between a hose and a cylinder. It is drawn as a two-position valve with an adjustable orifice in one position and a one-way check valve in the other. A spring holds it in one position but there are pressure feed pilot lines (dotted lines) feeding each end of the valve from opposite ports on the valve. This means that at low speeds while lowering and always while raising the cylinder, the valve stays open. However, if the hose was to break the cylinder started dropping quickly, the pressure difference across the orifice would cause the valve to switch, such that the check valve would block the pipeline. This would stop the cylinder from falling further. Therefore this is a hose burse safety protection valve.

The check valve is used to isolate the pump from backflows from the circuit, it also helps to keep the pump primed if components are removed. As the orifice size is reduced the pressure upsteam of the orifice will increase. The pressure is also sensed on one end of the directional valve (along dotted line) which will push the valve spool against the spring and therefore vent the circuit, maintaining a constant pressure on the pump.

Hydraulics engineers regularly encounter these diagrams, but these symbols can be daunting to interpret if you have limited experience with schematics and the fluid power industry.

On this page, Carr Lane ROEMHELD provides a comprehensive table outlining the definitions of each symbol used in a hydraulic diagram. Engineers can use this page as a reference to determine common schematic symbols used in fluid power, hydraulics, pneumatics, diagrams and circuits.

When it comes to safety system controls, SigmaHLR. leads the way in providing the most reliable, innovative, high quality products. Over the past five decades, our line of SigmaHLR products has set the industry standard for dependable pneumatic and hydraulic instruments. Serving the oil and gas industry worldwide, we offer proven products, quick delivery and the highest level of customer service.

Hydraulic circuits can be comprised of an infinite combination of cylinders, motors, valves, pumps and other equipment connected via hydraulic pipes and tubes. The complexity of these components are difficult to represent fully, so a family of graphic symbols have been developed to represent fluid power components and systems on schematic drawings.

The symbols do not identify component size or their actual position on the machine, however the symbols do provide vital information relating to the configurations and flow path connections.

Below we have summarised some of the most common symbols you may come across. Our technical sales engineers will be happy to help should you need any further help and assistance. Please get in touch on +44 (0)845-644-3640.

Below are some common illustrations of equipment located on fluids circuit diagrams, followed by descriptions of the most common elements. Later in this article series we will describe some simple hydraulic and pneumatic circuits composed of these circuit elements.

Needle valves are used to throttle or shut-off flow of fluids. They usually will vary flow with pressure or viscosity change. Some valves can be pressure and/or temperature compensating.

Flow control valves are used to control oil flow in one direction and unrestricted in the opposite direction. "Metered in" control means that the flow controls are controlling the fluid into the actuator, "metered out" is controlling the fluid out of the actuator. Some valves can be pressure and/or temperature compensating.

When the pilot line to a pilot-operated check valve is not pressurized, flow is allowed in one direction but blocked in the opposite direction. When the pilot line in a pilot-to-open valve is pressurized, the check valve is open, allowing flow in either direction.

When the pilot line to a pilot-operated check valve is not pressurized, flow is allowed in one direction but blocked in the opposite direction. When the pilot line in a pilot-to-close valve is pressurized, the check valve is closed, blocking flow in both directions.

Counterbalance valves are used to control overrunning loads and to support loads should a function be stopped at any point throughout its travel. NOTE: this valve is typically preset and should not be tampered with.

Flow fuses are normally open valves which close if the pressure difference between the inlet and outlet valves is too high compared to the design setting. The valve can be reset by reversing the direction of flow. When placed inline with an actuator (for example, a cylinder), flow fuses limit the maximum speed of that actuator.

Directional control valves are used to direct fluid flow into the appropriate lines for the designated operation. These valves are usually electrically controlled.

Hydraulic pumps are used to pump oil from the power unit to other parts of the hydraulic system. Some pumps have control options such as pressure or flow compensators.

Water modulating valves are used for controlling the oil temperature in the reservoir automatically by controlling the volume of water going through the heat exchanger.

Heat exchangers are used to remove heat from the circulating oil in the hydraulic system. The most common heat exchanger is water-to-oil but some times air-to-oil units are used. Coolers will cool the fluid.

Proportional valves are electrically controlled hydraulic valves. These valves proportionally control the hydraulic pressure and/or flow based on an electrical input signal.

For more information about reading hydraulic and pneumatic circuit diagrams, read the next article in this series which describes sample hydraulic circuits, or contact your Valmet representative.

The primary purpose of a safety valve is to protect life, property and the environment. Safety valves are designed to open and release excess pressure from vessels or equipment and then close again.

The function of safety valves differs depending on the load or main type of the valve. The main types of safety valves are spring-loaded, weight-loaded and controlled safety valves.

Regardless of the type or load, safety valves are set to a specific set pressure at which the medium is discharged in a controlled manner, thus preventing overpressure of the equipment. In dependence of several parameters such as the contained medium, the set pressure is individual for each safety application.

Our check valve products are designed to be self cleaning and positive sealing. We offer a wide range of sizes, cracking pressures and seal options in our standard product line. We also manufacture custom check, custom relief, custom manifolds, cartridge, non return, tank, needle, ball, valve pistons, cylinder, oxygen, bleed valves, poppets and more.

Industries: Medical, Dental, Aerospace, Automotive, Oil/Gas, Cryogenics, Chemical Processing, Agriculture, Pneumatics, Hydraulics, Food/Beverage, Fire Protection, HVAC, and More!