reason for connecting (short) pump inlet & outlet 4

[usman74]

hello mechanical engineers!!!
I'm an Electrical professional working at power plant where i have to deal with mechanical equipment too, like pumps, HX etc....
here in plant there a pump producing high pressure, around 20MPa while suction pressure is only 0.2 MPa. thus there is 19.8 MPa delta across the pump. due to that huge pressure difference a small line of shorted inlet & outlet. i checked pressure of shorted line which is only 0.3. i ask one of the mechanical engineer about it, he told me this line gives protection against huge pressure difference. but it is far from my understanding as it recover only 0.1 MPa. is my colleague right about it??? if yes than what is science behind it??? if not than what could be actual reason to shorten the pump inlet & outlet???
looking forward for reason with best regards.

 

[GHartmann]

Can you give a better description of what you mean by "a small line of shorted inlet & outlet".

It is unclear exactly what you are describing

 

[usman74]

a line of small diameter (comparing to suction & discharge lines) used. it connect the suction line directly to discharge line over the pump.

 

[usman74]

Ghartmann uploading picture

 

[GHartmann]

That does not look like it connects directly from the discharge to the suction. It looks like it is some type of leakoff from the pump mechanical seal or if these are canned motor or mag drive it could be something from the internal circulation system.

But we cannot tell with a Manufacturer and Model number

You need to find the O&M manual and brush-up on the pump details

Your mechanical colleague really hasn't provided a good explanation.

 

[JJPellin]

That looks like a balance line to balance the thrust forces on the rotor and reduce the pressure on the mechanical seal on the outboard end of the pump. Refer to the FAQ on balance disk / balance drum (faq407-1306)

Johnny Pellin

 

[byrdj]

do you have a cross sectional drawing?
It might show something like the device describe in the link referanced by JJPellin

 

[1gibson]

It looks like the main purpose is as a plan 13, to reduce seal chamber pressure and create some flow to help remove heat from seal chamber area. Secondary purpose could be to adjust thrust (if there is a balance drum/disk.) Sectional drawing will tell you, if nothing is attached to the shaft and there is only a close clearance bushing, then it is just a plan 13. If there is some rotating member attached to the shaft, it is a balance drum/disk.

 

[LittleInch]

If your mechanical engineer said this line was "protecting against huge pressure difference", it sounds like the balance drum/disk to me. I'm not sure how you checked the pressure as there was no guage I could see unless that third line goes to a pressure transmitter / switch?? That is probably there so that any break in the balance drum/disk would be noted and to prevent excessive flow in this line would trip the pump.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[byrdj]

pressure in the short line should be pump suction so Fb is opposite Fh

 

[usman74]

dear JJPellin!
thumbs up for you! bravo

 

[usman74]

thanx byrdj