Seal Characteristics

Introduction

Due consideration should be taken of climatic, process, or other conditions that might adversely affect the performance of the safety valve. Installation must be undertaken by qualified technicians and to good engineering practice. In addition, the user’s attention is drawn to our joint responsibility to ensure that the Health and Safety at Work Act is not contravened by incorrect installation, commissioning, or servicing.

It is important that the valve to be installed is correct in every aspect, i.e. set pressure, size, material type, etc. for the application.

 

Storage or Valve Before Installation

Valves should be stored preferably between 5°C and 25°C and at a relative humidity of less than 75%. Very moist or very dry conditions should be avoided. If a safety valve is installed after six months, or more, of storage, it must be subjected to a functional test before commissioning.

Thread protectors should not be removed until immediately prior to testing or installation, as they also prevent the ingress of foreign matter which could harm the valve.

 

Installation

VALVE INLET: Under no circumstances should it be possible to isolate the safety valve from the protected system. Safety valves should be mounted as close as possible to the protected system. The connecting pipe should be straight and as short as possible. The inlet line to the safety valve should have an effective area of flow at least equal to that of the safety valve inlet. Seetru Limited should be consulted if the safety valve is to be mounted in any position other than vertically. The maximum pressure drop through the inlet line to the safety valve should not exceed 3% of the set pressure when the valve is discharging at its rated capacity.

VALVE OUTLET: No isolating devices shall be fitted to the outlet pipe. Discharge pipes should be as short as possible and of such a size that the pressure developed therein will not reduce the relieving capacity. Ensure arrows indicating the direction of flow are pointing in the correct direction. The cross-sectional area of the discharge pipe should not be less than the area of the safety valve outlet.

Where safety valves are discharged into a manifold, the manifold must be capable of accommodating the simultaneous discharge of all valves connected to the manifold. Atmospheric discharge or discharge pipes should terminate at a location that will not cause a hazard to personnel, with particular attention being given to hazardous fluids or particles.

GENERAL: Inlet and outlet piping should be capable of supporting the safety valve so that no unacceptable mechanical load or vibration is transmitted to the valve, and be sufficiently strong to withstand the effects of the reaction forces when the valve is discharging.

All pipework or pressure vessels to which the safety valve is connected should be thoroughly cleaned before fitting the safety valve, to ensure that foreign matter does not pass through the valve. Particular care should be taken with the use of sealing compounds and P.T.F.E. tape to ensure that they do not enter the valve.

Atmospheric discharge valves should not be painted or coated with any substance that could obstruct or restrict free and full discharge through the valve. Suitable protection should be provided to prevent environmental build-up of ingress of foreign matter. Any condition that could lead to a blockage of discharge piping or discharge ports on safety valves must be avoided.

Where appropriate, discharge pipes should be provided to allow the discharge of fluid or gas to be piped away to a place where it does not present a hazard.

Where there is a possibility of a liquid head forming in a discharge pipe, a drain should be provided which leads to a safe discharge location.

To prevent unnecessary lifting of the safety valve it is recommended that there is a margin of at least 10% between the maximum operating pressure and the set pressure of the safety valve.

Functional Testing

Once installed in service, valves should be tested at least once every six months to ensure free movement of parts. This should be carried out by operating the easing gear when the valve is under a pressure of not less than 75% of the set pressure. Where valves are supplied without easing gear, the test should be in accordance with the full functional test described below.

Due regard must be paid to the safety of personnel. Testing should not create a hazard, with particular attention being given to foreign matter located in discharge outlets and other locations. When valves are installed in extreme operating environments, e.g.:

• hot, dry, dusty or high-humidity areas;
• oil, tar, or gummed deposits;
• sand, grit, earth, cement (construction, quarry, or similar sites);
• pollution-laden atmosphere (chemical works);
• any area where the valve can become contaminated with foreign matter likely to obstruct free and full discharge through the valve;
  the frequency of testing must be increased.

THE FREQUENCY OF THE TEST MUST BE ESTABLISHED BY THE USER TO SUIT EACH INSTALLATION OR PROCESS. DISCHARGE OUTLETS OF THE SAFETY VALVE MUST BE KEPT IN A CLEAN CONDITION, FREE FROM DEPOSITS OR BUILD-UP OF FOREIGN MATTER.

 

Full Functional Test

Safety valves should be checked every 12 months for correct function and test of set pressure, full flow, and reseat pressures. Ideally, the valve should be removed from the system and tested on specific test equipment. Before dismantling any pressurized components the system must be effectively isolated from all sources of pressure and completely vented to the atmosphere. When safety valves are taken out of service, care must be taken that the plant remains secure. Parallel or replacement safety devices of at least the same capacity must be provided. Where a safety valve does not meet the specification it must be refurbished, or replaced. If the valve is not functioning correctly, i.e. noisy or ‘hammering’ refer to Seetru Limited.

WE RECOMMEND THAT ADJUSTMENTS, MAINTENANCE, AND REPAIR OF SAFETY VALVES, INCLUDING CHANGES IN SET PRESSURE, SHOULD ONLY BE PERFORMED BY SEETRU OR AN AUTHORISED REPRESENTATIVE.