accumulator safety valve free sample

In order to ensure that the maximum allowable accumulation pressure of any system or apparatus protected by a safety valve is never exceeded, careful consideration of the safety valve’s position in the system has to be made. As there is such a wide range of applications, there is no absolute rule as to where the valve should be positioned and therefore, every application needs to be treated separately.

A common steam application for a safety valve is to protect process equipment supplied from a pressure reducing station. Two possible arrangements are shown in Figure 9.3.3.

The safety valve can be fitted within the pressure reducing station itself, that is, before the downstream stop valve, as in Figure 9.3.3 (a), or further downstream, nearer the apparatus as in Figure 9.3.3 (b). Fitting the safety valve before the downstream stop valve has the following advantages:

• The safety valve can be tested in-line by shutting down the downstream stop valve without the chance of downstream apparatus being over pressurised, should the safety valve fail under test.

• When setting the PRV under no-load conditions, the operation of the safety valve can be observed, as this condition is most likely to cause ‘simmer’. If this should occur, the PRV pressure can be adjusted to below the safety valve reseat pressure.

Indeed, a separate safety valve may have to be fitted on the inlet to each downstream piece of apparatus, when the PRV supplies several such pieces of apparatus.

• If supplying one piece of apparatus, which has a MAWP pressure less than the PRV supply pressure, the apparatus must be fitted with a safety valve, preferably close-coupled to its steam inlet connection.

• If a PRV is supplying more than one apparatus and the MAWP of any item is less than the PRV supply pressure, either the PRV station must be fitted with a safety valve set at the lowest possible MAWP of the connected apparatus, or each item of affected apparatus must be fitted with a safety valve.

• The safety valve must be located so that the pressure cannot accumulate in the apparatus viaanother route, for example, from a separate steam line or a bypass line.

It could be argued that every installation deserves special consideration when it comes to safety, but the following applications and situations are a little unusual and worth considering:

• Fire - Any pressure vessel should be protected from overpressure in the event of fire. Although a safety valve mounted for operational protection may also offer protection under fire conditions,such cases require special consideration, which is beyond the scope of this text.

• Exothermic applications - These must be fitted with a safety valve close-coupled to the apparatus steam inlet or the body direct. No alternative applies.

• Safety valves used as warning devices - Sometimes, safety valves are fitted to systems as warning devices. They are not required to relieve fault loads but to warn of pressures increasing above normal working pressures for operational reasons only. In these instances, safety valves are set at the warning pressure and only need to be of minimum size. If there is any danger of systems fitted with such a safety valve exceeding their maximum allowable working pressure, they must be protected by additional safety valves in the usual way.

In order to illustrate the importance of the positioning of a safety valve, consider an automatic pump trap (see Block 14) used to remove condensate from a heating vessel. The automatic pump trap (APT), incorporates a mechanical type pump, which uses the motive force of steam to pump the condensate through the return system. The position of the safety valve will depend on the MAWP of the APT and its required motive inlet pressure.

This arrangement is suitable if the pump-trap motive pressure is less than 1.6 bar g (safety valve set pressure of 2 bar g less 0.3 bar blowdown and a 0.1 bar shut-off margin). Since the MAWP of both the APT and the vessel are greater than the safety valve set pressure, a single safety valve would provide suitable protection for the system.

Here, two separate PRV stations are used each with its own safety valve. If the APT internals failed and steam at 4 bar g passed through the APT and into the vessel, safety valve ‘A’ would relieve this pressure and protect the vessel. Safety valve ‘B’ would not lift as the pressure in the APT is still acceptable and below its set pressure.

It should be noted that safety valve ‘A’ is positioned on the downstream side of the temperature control valve; this is done for both safety and operational reasons:

Operation - There is less chance of safety valve ‘A’ simmering during operation in this position,as the pressure is typically lower after the control valve than before it.

Also, note that if the MAWP of the pump-trap were greater than the pressure upstream of PRV ‘A’, it would be permissible to omit safety valve ‘B’ from the system, but safety valve ‘A’ must be sized to take into account the total fault flow through PRV ‘B’ as well as through PRV ‘A’.

A pharmaceutical factory has twelve jacketed pans on the same production floor, all rated with the same MAWP. Where would the safety valve be positioned?

One solution would be to install a safety valve on the inlet to each pan (Figure 9.3.6). In this instance, each safety valve would have to be sized to pass the entire load, in case the PRV failed open whilst the other eleven pans were shut down.

If additional apparatus with a lower MAWP than the pans (for example, a shell and tube heat exchanger) were to be included in the system, it would be necessary to fit an additional safety valve. This safety valve would be set to an appropriate lower set pressure and sized to pass the fault flow through the temperature control valve (see Figure 9.3.8).

Value pairs located in the areas of the characteristic curves with gray background cannot be realized with the safety valve. The characteristic curves shown here are only valid for a counter pressure of 0 bar in the discharge line.

In principle, the valve should be operated without counter pressure in the discharge line, if possible. In case of counter pressure in the discharge line, the maximum possible flow is reduced. There is a relationship between maximum counter pressure pT in the discharge line and flow qV, which can be seen from the following characteristic curve. Characteristic curves for intermediate values of the response pressure which are not listed must be determined by means of interpolation.

Diagram for determining the maximum counter pressure pT in the discharge line at port T of the valve dependent on the flow qVmax for valves DBDS 6...1X/...E with different response pressures pA.

Diagram for determining the maximum counter pressure pT in the discharge line at port T of the valve dependent on the flow qVmax for valves DBDS 10...1X/...E with different response pressures pA.

Diagram for determining the maximum admissible counter pressure pT in the discharge line at port T of the valve dependent on the flow qVmax for valves DBDS 20...1X/...E with different response pressures pA.

Diagram for determining the maximum counter pressure pT in the discharge line at port T of the valve dependent on the flow qVmax for valves DBDS 30...1X/...E with different response pressures pA.

Accumulator accessories are tools and equipment used to enhance the performance of hydraulic accumulators. Examples of accumulator accessories are safety blocks, repair tools and adapters, mounting hardware, gas boosters, and charging and gauging assemblies.

Safety blocks safeguard hydraulic accumulators. They possess a shut-off valve that segregates an accumulator from a hydraulic system for safety or maintenance reasons. Bladder pull rods, core tool, and a spanner wrench are among hydraulic accumulators’ repair tools. Mounting bases, clamps, u bolts, and spacers are mounting accessories for hydraulic accumulators that enable simple, secure, and special fastenings for static and dynamic stress applications. Charging and gauging assemblies ensure safe and secure pressurization and depressurization of accumulators. Gas boosters assist in the pre-charging of accumulators up to the rated pressure of the booster despite whether the source is pre-filled nitrogen gas bottles or an in-house nitrogen generating system.

Hydraulic accumulators’ safety blocks serve as the valve vital for the maintenance and safeguarding of the hydraulic system as well as emergency shut-off devices or pressure relief valves in the case of a hydraulic system malfunction or over-pressurization. It is also responsible for isolating the accumulator during maintenance of the system.

Safety blocks merge all the features required to safeguard, confine, and discharge a hydraulic accumulator. The shut-off valve rotates through 90 degrees to separate the accumulator instantly from the hydraulic system, in an emergency or for maintenance purposes. Once separated, the accumulator can be released to a tank via a manual or electrically controlled discharge valve. A PED-approved tamper-proof pressure relief valve provides additional system protection.

Safety blocks allow a safe, simple connection of an accumulator to a hydraulic system. They are applicable for use with all types of accumulators like bladder, piston and diaphragm. Their compact, multi-function design saves space and lessens connections. By reducing the time required for installation and maintenance procedures, safety blocks increase productivity and functionality, while system downtime is kept to a minimum. A full range of adapters is available to suit all standard port sizes and styles designed to simplify installation. The safety block should always be attached as close as possible to the accumulator. Only qualified personnel should perform the commissioning and maintenance of safety blocks and similar equipment.

Bladder pull rods come in different sizes and lengths to fit the different sizes of bladder accumulators. The pull rods are connected to the gas valve of the bladder to facilitate assembly into the shell.

Mounting accessories are tools that enable a secure and straightforward fastening of all hydraulic accumulators. These include u bolts, mounting clamps, and mounting bases. U Bolts are for horizontal or vertical mounting without a matching base. They are sold as a complete kit with stop nuts and washers.

Mounting clamps with rubber lining are for accumulator stabilization and electrical insulation. For the best support, combine the clamps with mounting bases.

Hydraulic accumulators employ charging and gauging equipment in order to charge bladder, piston or diaphragm type of accumulators with nitrogen. The use of these charging and gauging assemblies is also crucial in determining the pre-charge pressure of an accumulator to safeguard the efficiency and life of your hydraulic system.

The handling and loading of the equipment must be performed by qualified personnel. The accumulator should first be isolated from the hydraulic system, and the fluid side discharged before taking any readings or pressurizing with nitrogen. Use only nitrogen to pressurize the accumulator and never charge the accumulator with Oxygen.

● 3000 PSI Accumulators – AI-CG3-3KT-SS Charging & Gauging Kit are only for use on accumulators with pressure not higher than 3000 PSI. Use dry nitrogen gas only.

● 4000, 5000, & 6000 PSI Accumulators – AI-CG6-6KT-SS Kit are only for use on accumulators with pressure not higher than 6000 PSI. Use dry nitrogen gas only.

● 3000 and 6000 PSI Monitors units are designed to be permanently mounted on the valve stem of the accumulator to monitor the pressure of the hydraulic system continuously. Nitrogen pre-charge can only be determined when the hydraulic pressure is 0 PSI.

● Nitrogen Regulators The use of a nitrogen regulator is highly recommended to users pre-charging an accumulator. Nitrogen regulators guarantee that nitrogen is added to the accumulator at a safe rate, thus protecting the bladder from damage and keeping the air temperature inside the accumulator from increasing during compression. There are different types of nitrogen regulators to suit your accumulator.

Nitrogen Gas Boosters function as a support in the pre-charging of any accumulator up to the desired pressure of the booster. There’s a full line of nitrogen gas boosters that will suit your requirement and will fit any type and size of the accumulator, be it bladder, piston, diaphragm, and float type.

The primary function of a gas booster is to boost the pressure of storage cylinders from high-pressure to outlet pressures as high as 10000 psi. The goal is to secure a steady supply of maximum outlet pressure even if the storage pressure declines to 500 psi. Bootstraps act as the compressed air source where the gas boosters derive its high-pressure nitrogen supply. Gas valves and gauges are attached to the booster and mounted on an aluminum tube frame.

Accumulator accessories, as detailed above, are necessary for isolating, charging, mounting, monitoring, installing, and replacing most manufacturers’ hydraulic accumulator units. For assistance in determining the exact type and size of the accumulator for your application, contact us for help.