Pulsating pressure after plunger pump

[Austrian Lukas]

Hello,

I am a student and am doing my master thesis on membrane separation. The lab-scale membrane plant works with a CAT plunger pump (model 231) that enables flows of 8.7 lpm (2.3 gpm). The pressure I am working with is usually around 12 Bar (170 psi). The whole plant is designed to hold pressures up to 64 Bar, even though the pump can do up to 103 Bar (1500 psi). After the pump a pulsation damper is installed:

When I started my work several months ago everything was working fine. At one point however (after working at higher pressures between 50-60 Bar (800 psi) for a few hours), the pressure of the flow after the pump started pulsating +/- 2 Bar (30psi) and I could not find a solution for this problem. This pulsation was clearly visible on the analoge pressure gauge. The pulsation is smaller at lower pressures and increases at higher ones. At 30 Bar (430 psi) and higher the pulsation suddenly stops and the pressure becomes stable.

I tried cleaning the plant using NaOH and later H2SO4 as I suspected that maybe parts of the feed might have clogged some of the pipes. However, that did not help.

Due to the pulsation I can not continue with my experiments, as the pressure needs to be stable to obtain representative results. Also I am afraid that the problem gets even worse if I continue to use the plant like this.

Does someone have an idea what could be the problem here? I would be really thankful for any suggestions!

 

[LittleInch]

You need to look much more closely at your pulsation damper and how it is set up. Without knowing how this works a damper able to operate between 15 to 60 bar is not common.

Most of these dampers have some form of gas filled bladder or piston and hence at 60 bar, has a lot less gas volume to play with than at a lower pressure.

If you can priovide some details of the damper then we might get somewhere.

Also check the gas pressure ( if you can safely) inisde the damper/

If this is a spring device then the same applies - whilst the pressure rating of the damper can be high, the operating range of them is often different or the gas volume needs to be adjusted.

Running the pulsation damper outside of its normal range may have damaged it.

Or maybe your pump needs servicing? Have you read the manual?

https://www.catpumps.com/sites/default/files/products/pdfs/3FRSvc.pdf

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Austrian Lukas]

Thanks for your reply!

I have now checked the pulsation damper. Sadly, there is no pressure range printed on it. It says "180 Bar", I assume that is the maximum pressure. I will try to contact the supplier of the membrane plant on monday to see if I can get any data sheets of the damper. So far my search online was not successful as there was only little information printed on the damper. The temperature range is given to be -10 to 80 °C, so that should not be the problem (I heat up my feed unto 60°C).

I don't think I can check the pressure inside the damper, but I will ask our mechanic next week. I am not too confident that we can do that here at university though.

Do you know if the problem could be caused by air entrapped in the damper? (it might be worth mentioning that it is installed vertically)

I am sure though that I have only operated the plant at pressures & temperatures that are allowed according to the whole plant specifications.

I have read the manual before, but since the plant is only used for few projects the pump was definitley not used for many hours. Also, I have checked the oil level and it was slightly higher than the mark, so I assume that a lack of oil could not be the problem.

 

[akkamaan]

How would an added variable orifice plus a second damper/accumulator downstream the orifice? The orifice will dampen the pulsation and the second damper will finish the job. The problem with this is that you might have to increase the pump pressure since the orifice will cause a pressure drop when we have a flow.
Another way would be to have the damper in series instead of "T"-ed in...

 

[LittleInch]

The only other issue may be the number of flexibles you seem to have. Pulsation is a complex field for a piping system and the flexibles may be more "flexible" at certian pressures than others. Perhaps try a different flexible or make sure it is fixed in position. Or try some solid piping if you can.

But anything you can find on the damper (vendor, model no etc) is your best initial port of call. without knowing what the damper looks like it's not easy to say if trapped air would be an issue.

At higher pressures one of them might just get locked more and stop resonating.

I don't know if your PD look like this

http://catpumps.co.uk/products/pdfs/6013_E.pdf

But a bit of searching has found that operating range max limits are around 1:3 or 1:4 max, but charge pressure can be varied to give optimum performance at a particualr pressure. CAT quote pre charge pressure of 60% of operating pressure. However clearly if your operating pressure goes all over the place then your pre charge pressure needs to to do the same, or use a few different dampers

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Austrian Lukas]

@akkamaan
Thanks for your suggestion! However, I don't think changing the setup is the way to go here. As I have described, the plant worked fine during my first experiments. Also my colleagues, that worked with the plant before, did not experience this issue. I therefore think that something is broken. Changing the setup might solve this for now, but on the long term identifying what is broken and finding a solution for it seems more reasonable to me.

(also thanks for the suggestion of inserting the image, I hope the thread is more clear and structured now)

 

[LittleInch]

You might have damaged the damper if it was set for operating at 10-15 bar.

An easy item to fix or at least check and then move onto the next item if that doesn't work

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Austrian Lukas]

So I have found out that we currently don't have the tools necessary to adapt the pressure in the damper. However, I have contacted a company that might be able to supply those tools. Also I will try to find out what a new damper (optimized for my pressure range) would cost.