Single Pump or 2 Pumps Running with VSD?

A pump/motor is more efficient when operated near it's design efficiency, which is many times 80-90 % of full volume. But you must check with the pump and motor manufacturer. They should be proud enough of the package to give the maximum efficient point for the combined unit. That will aid you in selecting the best combination. I, too suspect the two smaller pumps will be better, and the two pumps give some redundency in case of failure of one pump, and the ability to maintain one pump if necesary without shutting the system down. (assuming there are isolation valves) I never like to see all of a system in one basket as it would be with one big pump.

Suggest 2 pumps. Run one of the pumps at 100% and control the other via the VSD. Running a DOL motor lightly loaded is inefficient. Make sure the motor you allocate for VSD is suitable for the duty or program into the VSD not to run lower than about 20Hz. Generally the motor cooling comes from the fan at the back and if it ain't turning you are not cooling.

As has been pointed out a single pump is sudden death in the event of failure.

Dear Mr.nmahadi,

Prima facie of the Issue - MAX EFFICIENCY with Minimum Cost. Any equipment should work to optimum capacity to achieve highest Efficiency hence, considering your Details 2 nos. of 4.2 MLD pumps will be the best option.

If you have one 8.4 MLD, majority of the days, the pump will work below 50% capacity, which is not advisable. If 4.2 MLD pump is working it will have 90% capacity which will have highest efficiency point.

DHAYANANDHAN.S

This is quite different from previous descriptions. You should clarify, with details and perhaps a sketch, what you are really trying to do.

You will need to post the Q>H curve of the Pump at different rpms. Then only can CR4 friends help you decide. Also you need to say 1 Pump or 2 pumps ( assuming you are still on the old Problem) . Mind you- the answer will be APPROXIMATE as the Pipe inside surface and pipe bends have to be assumed!

You want HIGH -TO-LOW level Flow RATE Booster Pumping .And again you are worrying about "Suction Head is VERY HIGH- will it start" ??

Indeed; it will start on its own, unless stopped by valve arrangements.

Just be sure to keep your 2 raw water inputs well separated. If you will have piping at the input then branch it (1 pipe --> Y --> 1 pipe for each pump) as far away from the pumps as possible to avoid mutual interference, especially because pumps will run at different speeds.

brgds

Snel

Naturally 1 Pump at top efficiency point always-at any throughput. That is the whole purpose of VSD,

But But But -- Will there be enough head at low throughputs at low RPMs - Check That first!

Hi Mukulmahant,

top efficiency is not kept when you change thruput. With 2 pumps, one will be at the top efficiency point (50% of total flow or more) during the festival,the other pump will work with a smaller efficiency but also lower power.

If you go with (2) smaller pumps and the pumps are going to be connected in parallel, The pumps have to be the same size through out, so they are not working against each other.

Dear Mr.phoenix911,

Quite True. That is the Idea of Parallel Operation.

DHAYANANDHAN.S