Low Flow Rate Problem.

[Tadders]

Hi all,

I hope someone can shed some light on this problem I am having. I have just installed a new heating system to a production line. The system is as follows. I have an open bath containing 2000 Litres (440 gallons) of clean water. A centrifugal pump capable of pumping 90 Litres (20 gallons) a minute at a maximum pressure of 2.2 bar in installed directly below the bath. The water is pumped along 36 Meters (118 feet) of 20 millimeter (3/4”) copper pipe passing through a heater contained in a cylinder before retuning to the bath. The pipework rises over a wall about 3 Meters high. I calculate that the pressure losses through the whole system including all bends, valves, strainers etc should be less than 1 bar.

Now here is my problem, I am looking to pump 12 Litres (2.6 gal) a minute but the maximum flow rate I can achieve is 7 Litres (1.5 gal) a minute. A pressure gauge on the delivery side of the pump has gone off the scale at 1.5 bar (22psi). I have automatic air vents at the highest point on the system and I have checked that there are no air locks elsewhere in the system.

Does anyone have any ideas as to what might be causing this problem? Is the fundamental design flawed?

|------------->------------------>-------------------------|
| |----------<------------------<------------| |
| | | |
| | | |
| | | |
| | 3 Mtr | |
| | | |
| | | |
| | |~~~~~~~~~| -----------------
| | | water | | heater |
| | ----------------- -----------------
| |_____| |
|---------<---@----|
pump


Many thanks in advance.

Tony.

 

[25362]

tadders: is there, then, a possibility of a gas lock formed by air released while on heating cycles ?

 

[Yorkman]

I know this posting is a little late, and the problem may have been resolved but, 25362 brings to light a possilty of air trapped in the volute of the pump. Depending on the volutes orrientation it may not be easy to vent out. Just a thought.

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI

 

[katmar]

An air lock in the volute could explain a low flowrate, but not a high pressure at the pump delivery. From the trouble-shooting done so far on the plant it looks like a simple case of foreign material trapped in the pipe and causing a restriction. Not an uncommon event during commissioning!

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[Tadders]

Just to let you all know that this problem is still ongoing. I am awaiting a break in production so that we can disconnect the pipe at the inlet to the bath and see if we get an increased flow. I hope that this can be completed sometime next week. I will post the result.

 

[Tadders]

Eureka!!! Just goes to prove the old adage... check the simple things first. There were two automatic air vents installed on the system where the pipework rose over the wall. These were of an incorrect type and were installed 'in-line' and designed for steam!!!! Unfortunately, they had been installed under the lagging, with only the top showing so it was not obvious that they were the wrong type.

The flow rates are now more than adequate and the heating system is working perfectly… and my stress levels have reduced significantly.

I would just like to take this opportunity to thank everyone who offered help and advice on this problem.

Best regards,

Tony

 

[Artisi]

Good result - just reinforces the need to check for the "stupid" mistakes first up before getting too technical.

Naresuan University
Phitsanulok
Thailand