Diesel fuel relief valve 2

[McCormick93]

Need some ideas if anyone has expertise with diesel fuel systems:
I have three outdoor above ground bulk storage tanks for No. 2 diesel fuel. Each has a pump discharging into a common supply line. A check valve at each pump prevents backflow if one of the pumps fails. The system is idle most of the time.
When the weather gets hot, the pipes heat up and the fuel expands, causing leaks at mechanical joints. There is no relief valve in the system currently.
I'm concerned that if I put in a relief valve, at some point it won't reseat, then I'll have an open path back to one of the tanks, causing it to overfill if its pump fails.

The pump manufacturer's literature recommends a "pressure relieving check valve". I have not been able to find one on the market, and the manufacturer does not have a source.

Would it be better to put a backpressure regulator on a return line? Is there a standard design for a fuel system like this? Obviously I don't want to spend lots of $$.

Thanks

 

[sailoday28]

Have you considered an accumulator or an expansion tank (which might require air pressure) on the downstream side of the check valves?

 

[CRG]

TRVs (thermal relief valves) are typically used to control the pressure thermal pressure rise.

Do the TRVs need to be listed per ASME BPV?

If I recall, B31.3 does require listed valves, B31.4 does not. I have used Swagelok R3A valves for B31.4 designs inside containment area and Anderson Greenwood 81P when a listed valve is required or if valve is located outside of containment area.

 

[btrueblood]

I can't see how any relief valve operating on seperate tanks can prevent one stuck valve from causing its tank to overfill. Can you plumb the tanks to have a common outlet manifold (so that they will all seek the same level)? This could be independent of the pump manifold, if necessary, but would just need to be sized to allow worst-case backflow (through stuck check/relief valve) to slosh into the other tanks under worst-case minimum gravity head difference.

Ben T.

 

[pmover]

CRG posting is valid.

TPRV's are used in fuel systems such that all sections of piping system have protection from thermal expansion of fluid. basically, these tprv's protect the piping system from overpressure due to thermal expansion of the fluid (i.e. similar to an infant burping). the outlet of tprv's is to a small collection tank whereby the fluid/fuel is used for other purposes or pumped back into the storage tank.

good luck!
-pmover

 

[btrueblood]

pmover:

What happens when one of these TPRV's sticks open?

 

[EGT01]

McCormick93,

I really don't have experience in your application but seems that your problem is not so much which device to select but where should it discharge. Whether it is a thermal relief valve, backpressure regulator or pressure relieving check valve, any of these may have a potential to not reseat tightly. However, considering the fluid service, I would not have thought that would be a big concern since I would expect it to be a fairly clean, none fouling service.

Actually, I suppose you could argue a similar concern for the check valve not reseating in your pump discharge. But in that case, you would need a pump failure and check valve failure to allow potential backflow into a tank. Does this mean you have a centrifugal type pump?

For safety reasons, my choice would be to use a safety valve versus a backpressure regulator. As for a pressure relieving check valve, I have heard of drilling a small diameter hole (1/8" maybe) in the check valve flap to be acceptable as overpressure protection for thermal relief but that requires the upstream side of the check valve to be able to handle the expanding fluid.

Is there a downstream system to which you can discharge a relief valve instead of discharging back to your storage tanks? As an administrative control, would it be possible to drain or otherwise blow-out some or all of the liquid in the common supply line as you go into an idle period? Blowing out the liquid could raise additional overpressure concerns depending on where you can blow-out the liquid.

 

[sailoday28]

If you have a positive head on the pump suctions, why not run a small diameter pipe with an orifice back to the suction side of the pump(s) or tank(s). The orifice diameter should be minimized and could act as a stuck open thermal relief valve. However, flow thru the device will be negligible during pump operation.

 

[McCormick93]

Thanks to all for your ideas.
EGT01, there are all kinds of ways for an idle fuel system to foul if not maintained properly -- algae, gelling in cold weather, etc. I rather like the idea of the pinhole in the check valve. Any pressure release would involve minimal flow. And back flow in the event of pump failure would be negligible, as sailoday suggests.