condenser flow problems

[freonjohn]

I have a 30 hp condenser water pump(Taco) serving a trane 650 ton centrifugal chiller. The pump is located 1.5 feet below the sump of the cooling tower. I was called to perform start-up on the pump and set the gpm. The design for the condenser is 1800 gpm at 51 ft. head and 8 psi pressure drop across condenser barrel. The readings at the pump are 7 in. vacuum at impeller inlet and 18 psi on the discharge which = 49 ft head. according to the pump curve
i am pumping 1900 gpm. At the condenser i have a pressure reading of 12 psi inlet and 7 psi outlet = 5 psid but i need 8 psid. I have a 6" metraflex triple duty valve in-between the pump outlet and the condenser inlet and this is where i have a 6 psi pressure drop but the valve is set at 100% The triple duty valve was disassembled and inspected and appears to be in working order. According to the flow chart for the triple duty valve @6 psi drop at 100% open = 4000 gpm?? I called metraflex and they said i should only have a 3 psi pressure drop?

aany ideas or suggestions? If the pump is moving 1900 gpm but my design pd at chiller should be 8 psi and I only have 5 psi am i still moving 1900 gpm?

Thanks for any help.

 

[MikeHalloran]

The pressure drop across the condenser suggests a flow around 1422 gpm. At that flow, the valve should drop about 0.76 psi at 100pct.

That and the reported DP across the valve suggests that the pump discharge pressure gage is reading high.

How hard would it be to check all the gages, or use just one?



Mike Halloran
Pembroke Pines, FL, USA

 

[freonjohn]

All readings have been checked with one gauge to avoid inaccuracies.

 

[MikeHalloran]

Then I'm stumped. Sorry.



Mike Halloran
Pembroke Pines, FL, USA

 

[imok2]

Is the valve installed backwards? Even if the valve says it's 100% open can you be sure? If you disconnect the operator can you manually open more?

 

[imok2]

I noticed it has a spring for return of the check disk are you sure the factory installed the correct spring range or may have mislabeled the valve.

 

[SAK9]

Pressure drop thru an equipment is not an accurate indication of flow.You will be better off using something like an ultrasonic(clamp on type)to get a measure of the actual flow.Design pressure drop given by manufacturers generally applies to a dirty condition of the tubes.So it is quite possible that you have design flow at less than design pressure drops.

 

[sterl]

Is your condenser keeping up with the Chiller? Are they of corresponding design capacity? If you are flowing only 1400 GPM through the codnenser, the delta-T at full load will reflect that and that's an easy calcualtion to work back to USGPM.