Pump Questions

[CBraungart]

We are designing a heat transfer fluid piping system with 2 pumps running in parallel and another as a standby. If one of the pumps happens to fail or shut down and we still have fluid pressure going into that pump line, is the pump capable of withstanding the pressure of the fluid when the pump is not running?

 

[zdas04]

CBraungart,
Go back and re-read your post. You haven't said what pump technology you are using. You haven't said who's pump you're using. You haven't said what the MAWP on the pump casing is.

My answer to your amazingly vague question is "maybe".

David

 

[JJPellin]

I agree that more information would be nice. I will assume you are referring to centrifugal pumps. In the parallel configuration you describe, each pump should have a check valve on the discharge so that it won't spin in reverse if it trips off. If the check valve works correctly, when a pump shuts down, it will only see suction pressure. If there is no check valve, it will spin backwards. It could suffer damage if allowed to spin in reverse at full speed (or faster). If the check valve were placed on the suction side of the pump (not recommended) it would pressure up to full discharge pressure from the running pump. For an API pump, this would not normally be a problem since the suction flange and the piping up to the valve should be designed for that pressure. You need to get the maximum allowable working pressure for your pump and use the P&ID to verify what pressure it will see under various conditions (running, tripped, etc) and verify that it will not see any pressure which it is not designed to accommodate.

Johnny Pellin

 

[CBraungart]

We are Running Klaus Union SLM AHO 8x6x15-25T10 Centrifugal pumps with variable speed motors on them (Marathon 125hp 1800rpm TEFC). The pumps will be running at 1600GPM each in parallel. If you need any other information let me know.

-Chad

 

[BigInch]

Inlet flange rating,
Outlet flange rating.

I had a pump at a booster station in a mountain valley. The head going into the booster pump when it was running was drawing the total inlet pressure provided by the mountain head all the way down to 50 psi. That was well under the inlet suction flange 300# rating. When the pump stopped, the suction pressure could build up to the full head of diesel (SG = 0.825) all the wat to the height of the mountain at 1500 m (4920 ft) which equalled 1750 psig. Of course that was well over the inlet flange's pressure rating and we had to install a relief valve running to a tank to blow down that pressure to keep it below the flange limit. If you have a situation similar to that you might have a problem.

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[zdas04]

So you had to empty your whole reservoir through the PSV and then drain the pipe to 840 ft before the PSV would shut? I hope you had plenty of tanks at the bottom. Since turning the pump off is a normal operating condition, I'd think that the designers messed up their sums on the required MAWP on the pipe--must have been flatlanders.

David

 

[BigInch]

The pipe was fine. On the original data sheet no value was specified for the inlet pressure rating of the pump. A totally empty box where the value should have been. The mgfr apparently didn't ask and supplied a 300# rating. The pump discharge was speced to 900#. On the other side of the pump station. Fortunately there was a surge relief tank there for the discharge side of things already, so we just had to run a new line to that.

Now on the next project you can be sure we made engineering co specified both sides of the pump correctly. That one had a run of 150 km run at more or less sea level to the first booster, pumping up to 1500 m to the next booster, which pumped up another 1320 m climb to the summit (well an 18 km tunnel just under the summit) then downslope to 2100 m elevation distribution plant. That one was interesting, since it had a pig bypass at booster sta #2. Do you see it?

With the pig bypass opened at #2, bang .. full head from 0 to 2820 m elevation = 3300 psig on the discharge at booster sta #1 (2160 psig rating). We added a couple of valves and interlocks in that bypass, so that the #1 to #2 segment would not be loaded by the pipeline above #2 going to that 2820 m summit, and then just to be sure, in case the interlock failed, we installed a psv at booster sta #2 coming off the incoming segment from #1 and going to a relief tank; set that at 350 psig something, so anything above #2 would blow down to 350 and then the discharge at BS#1 wouldn't ever go over 2160. .... Uh huh.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[BigInch]

In fact, it looks like in that pipeline a 300# inlet flange at either pump station would be ok with the above inlet relief configuration, as long as booster station #1 inlet never closed while the marine terminal pump station continued to run up the pressure. It did get a shutdown signal, if #1 or #2 ESDed. I'll bet they got the pumps for each project mixed up!

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/