pump control queries

[kenny.chow.hk]

Hi All, it is my first time to ask engineering problems via. internet.

I am a mechanical engineer from Hong Kong and working in a E&M contracting company.

The following queries was made me trouble in a time.

There are 2 sets of duplicate fixed fire fighting pumps (one duty and one standby) and 1 set located at south pump room and 1 set located at north pump room. These pumps are same duty points(Flow rate: 4000L/min, pump head: 10bar) without VFD.

These pumps are used to boost water to a ring pipework connecting with fire hydrants.Upon the fire hydrant valve is open, system pressure will drop and duty pump will be started by pressure switch sensor for 10% system pressure drop.

Now my problems:-
The material of ring pipework is maximum working pressure at 16bar, I have to ensure only 1 duty pump shall be started all the time.
If both 2 nos. duty pumps at South and North pump room are started, the system pressure will come to 20bar (>working pressure).

Hope receiving the answers.

 

[PNachtwey]

We can't see the *png file.
I would study pump and system curves. Where the two curves intersect is the operating pressure and flow. Obviously can can't run both pumps at full speed. Adding a second pump will probably require slowing down the first pump to match the speed of the second pump. both pumps but it will be hard to provide input without pump curves.

Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

http://forum.deltamotion.com/

 

[TimSchrader2]

If your sure there is no need to have both pumps on you can use a relay or relays that only allows the Low voltage control signal to one motor contactor or the other. You could also have a bypass switch if there is a time when you may wish to have both pumps on.

You could also have a emergency press switch in the high press line as a back up to shut power to pumps off.

 

[3DDave]

The png isn't visible because it's called "???.png" Stick to letters and numbers for the name.

 

[LittleInch]

Set one pump to turn on at 10% below your system pressure and the second to come on at say 15% below your set pressure.

You need to explain the system a bit more as to why there are two duplicate pump sets. Do you need two pumps to operate in certain fire scenarios?

This seems a very basic question. Have you no controls engineers available?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.