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Home > Forums > Mechanical Engineers > Activities > Fluid Power engineering Forum

negative pressure in a circulation system

thread1083-319809
Read More Threads Like This One
YuriB (Electrical)
10 Apr 12 12:17
Is it normal to have continuosly negative pressure in a water chiller system - actually, along the whole suction line of the pump on the roof?  
MikeHalloran (Mechanical)
10 Apr 12 12:25
If you pump liquid in a closed loop, and you attach a reservoir that communicates with the atmosphere, that reservoir becomes sort of a reference point.  If it's attached to the pump suction, the entire loop will run at a positive pressure.  If it's attached to the pump discharge, the entire loop will run at a negative pressure.

... after everything stabilizes.
... roughly.
... absent other influences.
 

Mike Halloran
Pembroke Pines, FL, USA

YuriB (Electrical)
10 Apr 12 12:41
It is closed system. They are refilling it regularly but water is keeping running away. Now there is again negative P in the suction line on the roof.


 
MikeHalloran (Mechanical)
10 Apr 12 13:16
The negative pressure suggests that a leak, if one exists, is on the discharge side of the pump.

( or that's where the pressure compensator/ bellows/ diaphragm/ reservoir is )

Maybe it's leaking, or maybe it was designed that way.  
Do you have any design documents?

 

Mike Halloran
Pembroke Pines, FL, USA

YuriB (Electrical)
10 Apr 12 14:06
But such pump work is not normal, right ? (isssues such as cavitation, etc : pump sounded indeed terribly, and I did not dare to start the chiller today for the season). There often were found opulant brown foamy exudes from a degassing valve - I suspect microorganisms in the system - hope it's not legionella.
MikeHalloran (Mechanical)
10 Apr 12 14:29
A negative absolute pressure would be very newsworthy.

A negative gage pressure is perfectly normal in some parts of some systems.

Where is the operator's manual for your system?
 

Mike Halloran
Pembroke Pines, FL, USA

Compositepro (Chemical)
10 Apr 12 16:58
Chilled water loops should have an expansion tank at the low pressure point in the loop to accommodate the changes in fluid volume with temperature changes. This tank normally has a water pressure regulator near by that will add more water if pressure drops below set point (often 15 psi). It will also have an air vent to vent excess air that might accumulate.
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