How do you Purge a PSV, at the highest point in the line?

[Cee555]

How would you purge a PRV of air when it's on the highest point in the line? There is no air relief on the valve how do I make sure the air has been completley drained?

CH

 

[Cee555]

Yes that will be the max operating pressure.
Nominal not known, the customer will operate anywhere between the highest and lowest parameters denpendant on the supply demand at any given time. The system was sized properly. I suspect that the relief valves regardless of what the decription states, is not suitable for this high of flow. All the other components work fine.

 

[Zoobie]

This is not a code valve, but regardless, your set max operating pressure should be less than the set pressure (90% is typical for conventional valves). Anything above that and you are asking for problems. This valve may not be 'typical' but I will quote some typical data from API 520. Valves may simmer if the operating pressure is within 98% of the set pressure. This may in fact be the knocking that you mention. The closing pressure for a conventional PSV is typically 92.5% of the set pressure (as per API 520). This means that if the valve popped at 3200 psi you would need to get down to 2930 psi before the valve would close. Of course your valve may not have the same blowdown characteristics but you do need to consider this. Now when you throw in the sinusoidal issues that TSeener mentions you will be lucky if you can keep this valve closed operating anywhere near your set pressure.

 

[Cee555]

The valve can be manually adjusted, 3000 to 5000 PSI, I am testing water through this, the relief valve and line is 1/4" Tube with a 0.049 wall thickness, the relief valve piping is 2m total in length feeding back into the suction piping. The discharge size is 1/2", could the flow going through the smaller tube diameter be causing this hammering affect?

 

[TSeener]

Exactly Zoobie. The "Design Pressure" and "Operating Pressure" are two different numbers here, and they both can not be 3200 psig. Check with the pump manufacturer to find the maximum allowable working pressure (stated as if it was a vessel to make a point), because if the discharge pressure is 3200 psig, the pump can handle above that (and it sounds as if you have seen that).

If you are truly concerned about the valves capacity, you can confirm the relief valves relieving capacity using the orfice size of the valve, but I do not think that's your issue here.

Best Regards,

TSeener

 

[Zoobie]

Based on the information that you have provided (pump operating pressure = 3200 psi, PSV set pressure = 3200 psi, positive displacement reciprocating pump) my opinion still is the PSV setting. I don't think it has anything to do with the line size. Your discharge pressure is not a flat line (perhaps if your relief valve is after the pulsation dampner than you may be close) and your relief valve is probably chattering. The relief valve is changing the back pressure on the pump and you have a pulsing flow back into the pump suction. All of this is working together to make a mess (of course this is really dependent on where your dampners, valves, check valves etc. are).

It sounds like the system under normal operation works fine. When the valve is relieving it does not (please correct me if I'm wrong). Maybe we need to step back a bit...otherwise we will start assuming too much. What is the design intent of the relieving system? What was the criteria used to pick the set pressure?

 

[Cee555]

The PRV can be manually adjusted anywhere between 3000 and 5000 PSI, fully open the relief valve still knocks.
The design intent of the relief valve is to protect the equipment should the system extend beyond 3200PSI. I selected the Valve based on discharge and flow. It was very hard sourcing a relief valve that could operate at pressures above 1000PSI. In order to accomodate the high pressure I had to settle for a 1/4" size valve as oppose to my line sized which is 1/2".

 

[Zoobie]

Where is the pulsation dampner in relation to the PSV? What happens if you relieve the valve to atmosphere as opposed to the pump suction? With water this shouldn't be a hazard (as long as the high pressure water stream is not directed at anyone or anything).

If you have determined that your maximum allowable working pressure is 3200 psi than you should have an operating pressure below this (I would use 90% but the valve manufacturer may have some better closing pressure data that you could use).

You state that the valve knocks when it is fully open...at what set pressure and operating pressure is this?

How does the knocking frequency relate to the pump stroke frequency?

 

[sshep]

Cee555,
Still wondering about the process downstream of the pump, and what the process pressure is? If this is a modulating hydraulic valve rather than a conventional RV which relieves back to suction, then you seem to be doing the design properly per my experience. The problem does not seem to be your relief valve (assuming you have set this reasonably). Rather I feel, your process and piping is imposing some sort of backpressure at the pump which causes the pressure to rise to the relief pressure. If this is an injection system what are the piping, injection point, and process details?
best wishes, sshep

 

[Cee555]

sshep I think you might be right, my relief piping makes two sharp 90 degree turns I think I might be creating some back pressure there!!!

Zoobie the valve starts knocking in and around 3200PSI. When the valve is fully open the valve should relieve at 3000 PSI.

 

[sshep]

Cee55,
When I reread this I think maybe you are testing the relief of an injection skid vs actually operating one. Hopefully it will not be the intended operation to operate against the relief valve, but if so you must have a 'proportional opening valve'. Not sure what you have, but when I check out Ham-lets H900HP relief valve it does not say it is modulating. The description of this sounds conventional in nature.

If you expect continuous relief, I envision something more like a swagelok proportioning valve:

http://www.swagelok.com/downloads/webcatalogs/MS-01-141.pdf#search='swagelok relief valves'

First reevaluate your Ham-let, but if not then i have few other ideas: relief valve could chatter due to the inlet piping you describe (line loss swings pressure below set-point). Such chattering will likely be higher frequency than the pump. Might not take too much length of 1/4" inlet to cause this. Cavitation could cause vibration.

Best wishes, sshep

 

[Cee555]

You guys really know your stuff!!!
I could have used your expertice when I was a young pup starting out, and my then manager gave me a project selecting and pricing centrifigal pumps for waste water...of course being the cocky kid that I was, I took the project on...and man I failed miserably. When I left the company they were still working on warranty issues.

I will look at the Hamlet vs Swageloc...I was operating under the assumption that they were identical.