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

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

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

(OP)
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

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

What's normally in the line?

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

I really should finish thinking before I post...anyways, what type of valve is it.  If its a conventional valve I presume that it is not equipped with a test or lifting lever...perhaps this is what you refer to as the air relief.  

If its a pilot operated valve than you may be able to apply an external pressure to the pilot to trigger the valve.

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

(OP)
Its a standard PRV relief valve, Hamlet is the manufacturer.  How do we release the air trapped at the top of the relief valve?
we are testing water, but methanol will be the fluid.

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

I took at look at the Ham-let website just to get a visual of the valve...no bright ideas popped into my head.  Have you contacted Ham-let?  If purging all the air is absolutely crucial (based on some risk assessment) then perhaps you need a different valve or inlet piping set-up.

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

If you really want liquid in this leg you can place a vent valve at that point. Frequently a small bypass (i.e. to flare) is handy for depressuring some systems.

On the otherhand, if the system has been air freed with N2, there is probably no compelling reason to get the inlet line liquid full. Typically the PSV location is put at a high point for the purpose of relieving vapors anyway. Hint: air free your system by pressuring and depressuring with N2 so as to get airfree at all points.

Lastly, using the lifting lever to vent air from the system runs the risk of difficulty reseating. If you have a good seal at the PSV, you are best advised not to casually activate the lever.

best wishes, sshep

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

(OP)
Thanks guys!!!
Just a very noisy valve.

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

I agree with sshep in that a Nitrogen purge is a good start, but you may not be able to accomedate this type of operation.  What exactly would be the problem with installing it in the horizontal?  I have used these types of reliefs in all sorts of orientations and have not had any issues.  It does not require a vertical installation, since it is a spring loaded relief, correct?  I would recommend making sure that the relief line runs clearly away from the valve, so that a head pressure is not influencing the relief set pressure.

 You do not state the intent of this relief device and its location, which are critical factors in solving your issue.  If it is to protect against an overpressure from a pump, you will be fine by moving it into a horizontal orientation.  

I would also be very careful about the elastomers, as they will be your point of failure.  

Best Regards,

TSeener

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

TSeener, I would be a bit concerned about changing the orientation without consulting the manufacturer first (See API 520, Part II, Section 7.4).  

Sshep, thanks for the tip regarding lifting levers.

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

(OP)
Pump skids have been built and are currently in the testing phase.  Relief Valve is in the vertical position at the highest point in the discharge side to protect against over pressure.  The real problem is that the pulsation of the pump is causing the valve to open and close repeatedly when operating at high pressure.  I want to elinate all the other factors before settling on a possible solution which at this point appears to be a pulsation dampner.

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

I would be surprised if any air trapped would be causing your valve to lift in the situation you describe (because air is squishy).  In fact the air may actually reduce the pulsation...some pulsation dampeners simply used compressed air.  I have a feeling your PSV is actually doing what it is supposed to do.  

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

After talking to the manufacturer, they have no issues orienting the valve in any orientation.  Their primary concern would appear to be the solvent and the o-ring...  Any changes to the o-ring via swelling or distoring will cause failure (to open or seal).  Also, these types of valves do not meet any of the codes API or ASME, and the manufacturer(Ham-let) basically confirmed that for me.  Check out Swagelok, as they offer an identical design, and they say clearly that they are not rated per any code.

One item that is required is the rational for the setpoint, i.e. it is the maximum allowable pressure of the pump or the piping system.  The double diaphragm pumps generate a Sinusodal flow, resulting in a peak of 3 times the pressure of the typical hydraulic analysis.  The compression of the air is expected, however if the setpoint is set too low for this system, you will have releases. The pulse dampner will smooth the pressure spikes out to provide you with hydraulics that are more in line with your thoughts, but it will not make a bit of differnece if your pump is not appropriately sized.

Please let me know if you need any additional assistance.

Best Regards,

TSeener

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

(OP)
New Problem.
Even with a pulsation dampener on the discharge end of the plunger pump, the Relief Valve now makes a knocking noise at high flow?  Anyone know the cause of this, the PRV valve is sized properly.

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

Do you have a pressure gauge at the discharge of the pump?  If so, what is it doing?  Maybe you can provide some other numbers that may help us help you.  Things like PSV set pressure, pump pressures, etc.

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

Yes, even a brief description of the "system", what are you feeding with the pump (pressurized tank or a distillation column), line sizes, flowrates, pressures, etc... As much info as you can provide, including any sizing critera for the pump and the line sizes that you may have performed.  Also, you mention that the PSV is sized properly, well what was the sizing critera used to pick that specific valve?  

  There is a knock, but is there a discharge? With out the actual pressure data, it would be a guess at best.  

Regards,

TSeener

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

Cee555,
I know that there are some typical piping layouts for PD pumps to address momentum issues etc. Having the relief valve directly in line with the discharge can be a problem in some cases. I will try to find a reference, or perhaps others can. But I have a few questions as well:

1) What is downstream of this pump- i.e. can the discharge flow freely into the downstream process, or is there a control valve as well?
2) What type of PD pump (is is a double diaphram per TSeener), what frequency, what flowrate?
3) Did you charge the pulsation dampener with the required N2 pressure when you installed it (thinking of a bladder type per my experience)?
4) What is the relief valve set pressure, and is it a conventional relief valve.

A modulating hydraulic relief valve (vs conventional) is the only way to actually relieve an net accumulation in the discharge of a PD pump. Sometimes internal relief is considered good enough, but we often also spec something external. In these cases the hydraulic relief can simply be routed back to the suction. A conventional relief valve will not last long in a blocked in throttled discharge situation- after lifting a few hundred times it will fail, usually by failing to seat properly and continually flowing product to wherever you have routed it. If your system has been in operation for any significant length of time, you might also consider that the valve is already broken some way and need to be checked.

The sound you hear at the RV is not good, but you will be able to solve this if you keep at it.

best wishes, sshep

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

(OP)
Rated Pump flow = 0.32 USGPM = 0.07 m3/h
Discharge Pressure = 3200 psig = 22063 kPa

Plunger pump, 1/4" Ham let relief valve.
The pumps operate nicely up and untill they reach max pressure the piping starts vibrating, can't ge a good read as the gauge starts vibrating at this poing.

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

What is the PSV set pressure?

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

(OP)
3200 psi

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

The set pressure and the discharge pressure are the same?  You need to look at your system, and identify the weakest link, and the allowable working pressure is the set pressure.  I would expect that the pumps maximum allowable pressure is much greater than 3200psi?  I think that you will see my point here, but the set pressure needs to be much higher than your working pressure.   As I mentioned above, these types of pumps and other positive displacement pumps generate a Sinusodal Flow, which creates the pressure spikes.

The pressures and flows are good and justify the Hamlet, but the set point does seem a bit too close the the edge.

Please let me know if I can be of any additional assitance.

Best Regards,

TSeener

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

(OP)
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.

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

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.

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

(OP)
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?

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

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

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

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?

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

(OP)
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".

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

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?

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

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

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

(OP)
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.

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

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%20relief%20valves'

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

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

(OP)
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.

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