Pumps Capacity

[Samer2828]

We did install FLYGT Pumps. In theory the pump can give 16.4 lit / second at 5.1 m Head. We found out that the pump gives us 12 lit/sec only. What can be the problem??

 

[vishy]

I presume u r referring to a centrifugal pump.The system resistance against which the pump has to work may be higher than what u hd expected.This can be confirmed from the reading of the pressure gauge at pump discharge.You hv the following options:

1) Reduce the system resistance
2) Use higher dia impeller. This can be confirmed by the supplier.The motor size should be checked.

Hope u find these helpful.

Vishy.

 

[electricsub]

Samer,
I assume that the flow/head that you are looking for is the 16.4 l/sec at 5.1 mtrs.
The reduced flow you are getting could caused for several reasons, a few are :
1- How have you sized the "total delivery head" of 5.1 mtrs.
and did you use the correct number of bends,valve and pipe lengths, diameter of pipe, friction factor for the pipe used ??
2- Using a submersible pump, from what level did you measure the "static head " from for the pump, and to what level for the discharge point ?

3- Check the pump motor direction of rotation, before you do anything else, if its a Flygt and fitted with a 3 phase motor it should "Kick" anti clockwise (left) as you look from the top of the pump, on starting,you will most likely need to lift the pump out of the sump to check properly, if your experienced in what to look for. It the motor is larger than say 4.0 kewat, it may have Star/delta starting, if so there should be two kicks
( each about 6 seconds apart )

There are many other possible reasons, would need more info. to give additional help,just ask if you wish more help.

Good luck

Electricsub

 

[budbase]

I agree with electrisub that reverse rotation could be the problem. In my experience (40 years) as a Pump Specialist that happens way too often. Check the shut-off head, that eliminates a lot of other variables such as friction loss problems. if the shut-off head is around 75% of design you're running that puppy backwards.

 

[NumberCruncher]

I agree with those who responded above. The approach I would recommend is to . . .
1. Determine if the pumps are operating on their published curve.
2. Determine if there is air trapped in high spots in the force main.
3. Check your design. We all take shortcuts and assumptions that sometimes fail to model real world conditions. I have been using a software package called PS-1 that does a good job. You can download a trial version from CivilWorld.com in the hydraulics download section.