API 676

[vjr0512]

We are using API 676 vane pump for the fuel service . As per API 676, there is no insistence of the External pressure relief valve but asked to have a safety system like PCV or pressure limiting valve.. Vendors are giving internal relief valve inside the pump. How reliable is these internal relief valves? or should we insist for external pressure relief valve in addition to internal relief valve. This pump is installed in an independent package and there is no process system pressure acts on the package. This package supplies fuel to the helicopters in an offshore platform .

 

[Pumpsonly]

Pressure relief valve( PRV) , pressure limiting valve ( PLV) , Pressure control valve ( PCV) used in the PD pumps are all the same function is to prevent overpressure of the system or overloading the driver in the event that the discharge piping is blocked. The internal PRV , PLV, PCV what ever you call it provided by the pump makers are reliable as they are tested with the pump. But due to the relived flow is directly back to the pump suction chamber, the liquid can be heated up quickly.
Therefore there must some other instrumentation to shut down the pump fairy quickly.

 

[LittleInch]

Without seeing the sytem set-up it is difficult to comment and really depends on where the relief valve is and how easy it is to both check it's operation or replace in service. As pumps only says if the return path is direct to the pump sucton, any long term operation of the relief system will rapidly lead to heating up of the fuel which is not a good idea at all if this fuel is then released into the discharge line into a fuel tank.

I would insist of a temperature alarm / shutdown and also a high and HH pressure switch to shut down the system in the event the internal relief failed to operate correctly as these pumps, as I'm sure you know, can generate high presures very quickly if the phyiscal pressure relief fails to operate or becomes clogged. Most of the time though the issue is that the relief valve passes when it shouldn't and results in poor delivery pressure / flow. This is when ability to test and maintain the valve becomes important.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[DubMac]

ALWAYS install external relief valve on EVERY PD pump installation. Internal reliefs are meant to protect the pump itself and are not allowed to take the place of external relief valve, WHICH IS REQUIRED BY API. API 676 addresses the pump, there is another API spec I believe that covers relief valves. Good Grief man, you are pumping av-fuel on an offshore platform, PLEASE put relief valves on there.

I cannot imagine a system passing ABS, USCG, or any other of the regulating agencies offshore without a mandatory external relief valve. The vendor can supply the relief valve, but really it should be sized/selected under your eyes since it will be protecting your system.

 

[PumpSmart]

Internal RValve are reliable than pump itself.
But it is recommended to use another in the system , too.