Discharge pressure on submersible pump

[Ork1]

I am troubleshooting pump performance on a 58hp submersible Flygt pump. I want to install a pressure gage on the discharge pipe but the discharge pipe is flexible Goodall hose and is directly connected to the check valve. after the check valve it is 4" hard pipe. Should I drill and tap directly into the check valve? Any Ideas...

 

[Artisi]

is there a tapping in the discharge flange on the pump?

 

[Ork1]

Artisi,
I do not quite understand the question....

 

[Artisi]

Is there a drilled, tapped and plugged hole in the pump discharge flange, you can attach a pressure gauge at this point. Alternately, tap into the 4" pipe.

 

[Ork1]

Artisi,
Since the pump is totally submerged your suggestion seems to be good except wouldn't the check valve give erratic or inaccurate readings? In addition, would it make any difference if I cut a hole and welded a pipe coupling to the pipe and installed a gage from there? or, is drilling and tapping the way to go. I am pumping discharge mine water.

 

[Artisi]

You could weld a threaded fitting to the steel discharge pipe and place your discharge gauge there. You will need to add any height difference between the pump and the measuring point to give a fairly accurate discharge pressure at the pump, ie, if the gauge is 2 metres higher than the pump centreline add 2 meters to the pressure reading on the gauge - you may need to correct for pumpage SG if you are pumping slurry with an sg > 1.

 

[Ork1]

Artisi,
Thank you for the info. My chief concern still is the reading I will get positioning the gauge above the check valve. I don't have much of a choice in this situation. I would like to be as close to the pump as possible and yes, adding the two meters is correct but, what can I expect from placing the gauge above the check? I have not done this before and I am concerned with not getting an accurate reading. I suppose if there was a problem with the check valve at the same time I really wouldn't be able to tell if it was poor pump performance or a bad check valve. What other option do I have??
Thanks for hanging in there with me on this....

 

[Artisi]

Why do you need to be close to the pump - there is no good reason for this in the situation you have, you seem to want to establish if the pump is somewhere near to its performance - is this correct?

The check valve will have an influence on the reading - it will reduce the head pressure you see at the gauge - by how much will depend on the valve type or whether it is stuck partially closed etc.

Maybe a description of your problem might help in getting better advice.

If you consider that you have a real pump problem, ie reduced flow, it might be necessary to take the pump out of service for an inspection as measuring above the cv will not tell you whether it is a pump problem or the cv.

 

[miningman]

Unless you are using the pump to move water long lateral distances, the vertical head you are pumping against will be 85%+ of the actual head the pump sees. Put your guage anywhere convenient, above or below the check valve. What is the nature of you problem?? If it is low flow at the discharge, your impellers are wearing. Ignore theoretical differences in water SG, you are pumping normal dirty mine water, not slurry. The impellers can be adjusted by a competant millwright but by the time you've pulled the pump to change it out, its generally more effective to fully dismantle the bottom end and overhaul completely.

And if you think the bottom end is wearing, let the pump run continously. Lower end wear usually involves some wear on the seal between the motor and the pump. While running, there is some force applied to the seal that prevents water passing the seal. Turn the pump off for a few minutes, water by passes the seal, and when you restart it, bang, you need a motor rebuild as well as a pump rebuild.

 

[Ork1]

Thanks for responding, The pump is new and it is not performing, same model etc..as our other 58hp pumps. Dirty mine water and an uphill 2% grade for a mile underground in 4" pipe. I was tasked to install a gauge. I said I will put the gauge above the check valve. The engineer in charge asked me to install it directly in the middle of the check valve!!! Why, I do not know..... I asked him and he replied, "closer to the pump the better". I am trying to find out from other experts as to why.....

 

[Artisi]

new pump / installation ??
Is it running in the right direction.

In an ideal world the gauge could be placed at the discharge flange and would save you making a few assumptions as to what losses are invoved if the gauge was elsewhere in the system, otherwise no good reason for "closer the better"

Where is the cv in the system?

 

[Ork1]

The cv is 9 feet above the pump the pump is under 4 feet of water.

 

[Artisi]

If you tap into the pipe after the cv and get a pressure reading all you need to do is add 9ft to the pressure reading plus something for the lossses in the cv.

when you say not performing is this - low on flow or low on pressure or both.

Have you checked (DO NOT ASSUME) that the pump is operaing in the right direction - running in the wrong direction will still give you flow and can even give a high discharge pressure.

 

[Ork1]

Artisi,
Thanks, after I gathered more info. I was told the mine dewatering dept. are changing out pumps too frequently. That is all I know at the moment.