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

 

[Zoobie]

What's normally in the line?

 

[Zoobie]

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.

 

[Cee555]

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.

 

[Zoobie]

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.

 

[sshep]

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

 

[Cee555]

Thanks guys!!!
Just a very noisy valve.

 

[TSeener]

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

 

[Zoobie]

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.

 

[Cee555]

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.

 

[Zoobie]

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.

 

[TSeener]

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

 

[Cee555]

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.

 

[Zoobie]

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.

 

[TSeener]

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

 

[sshep]

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

 

[Cee555]

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.

 

[Zoobie]

What is the PSV set pressure?

 

[Cee555]

3200 psi

 

[TSeener]

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