Water Pump Performance

I assume it's like this one with an asynchronous (induction) motor.

Increasing the frequency increases the motor speed but reduces the current (motor torque or pump head). So to increase the flow rate and maintain the same maximum pressure, you would have to increase both frequency and voltage proportionally. (V/F ratio remains the same).

Having said this, be warned that you will be putting more stress on the pump and motor, and depending on how well it is designed, the lifetime may be reduced and it may fail prematurely.

OK thank you, Rixter. I thought it might be simpler - I do have an autotransformer and also a VFD but I wouldn't know which order to put them. I will hold off trying till I have more time to study the problem.

Maybe I'l just ask the pump maker if they have a 300 watter. Or wait till this one wears out, buy another brand that does.

Thanks,

Stuart.

VFD etc add to cost.Simple and cost effective solution will be to buy a new pumpset of reqired flow and head

Above base frequency (60Hz we assume) you don't increase the voltage. Increasing the voltage leads to non-linear losses that will crisp your motor in short order. Because you keep your voltage constant (at motor rated voltage), your torque capability drops according to the speed above base (constant horsepower range). If your motor is now lightly loaded, you could get more pump flow/pressure with a VFD, but the load rises quickly with speed, as JRaef notes. If your motor load now is over 50%, you may not see much improvement for your efforts.

Generally, permanent split capacitor, shaded pole & ac synchronous single phase motors can be operated with a single phase VFD. Leeson make one, among others. They have a 2.4 ampere rated VFD in open enclosure that lists for $250, you won't get out of it for less than $100, most likely.

That is what’s called a “centrifugal” pump (aka “quadratic” load) meaning that the power required by the pump portion will increase at the CUBE of the speed change. So even if you increase the voltage and frequency together via a VFD and transformer, increasing the speed by just 20% requires 172% more power from that motor. If the motor was twice as large as it needed that could work, but as a general rule pumP manufacturers don’t do that, they size their motors based on an exact performance expectation.

You will overload it. You just need need a bigger pump.

PS: that appears to be a single phase motor as well, so using a VFD is likely out of the question anyway.

There are two things that will give more output without electrical modifications:

1. Reduce the back pressure on the output. If you are using spray nozzles, a larger size will reduce the pressure.

2. Reduce the lift on the input. Place the pump as close to the water source as possible.

You're right, Dave.

I found a major improvement by changing from a 1/2" hose to a 5/8". Can water the garden in less than 1/2 the time now.

I can't get the pump much closer to the water - in X & Y it is within a foot or two, & 'Z', just depends on the water table. Lets see how the dry season goes this year -

250 watt pretty weak...

You could have the pump fill a reservoir tank with float switch, then have the reservoir feed the intake of the pump when use is desired through a system of piping and valves...this would raise the suction pressure and boost the discharge volume...

adequate for local conditions. & 4 floors with a roof garden -

250 W is on the medium / high side for house pumps.

I guess that would depend on square footage....and elevation....

The only thing you can do is provide a pre-pump "pump" that delivers water to the pump at an increased pressure. This will allow the fully VOLUMATIC CAPACITY of the pump to deliver water.

AKA multistage pump.

Just 2 motors & 2 separate shafts, but otherwise...

No. Not a multistage pump but a simple centrifugal pump with an output greater than the maximum of the pump in this discussion.

If it was me and the choice was to scrap it or boost it. If I had the VFD and autotranny I would try to boost the output a little bit at a time - see what happens.

If you overdo it, and it 'burns' out on overload, as it might - then you scrap it - and get a new one the right size.

Although changing pipe size seems to have helped, so it might not need much of a boost, if at all, so might not overload - then change it when it wears out.

Converted to USD, that entire pump was worth about $244. A VFD for a single phase motor of that type (assuming the motor is PSC or Shaded Pole), is about $250, yet it may not work.

To my minds, it's likely less expensive to just buy a larger pump and be done with this...

Water lifting devices

You can do both. Sooner or later you will burn out either the motor or the wiring. It would be better for you to redesign the equipment properly so that the system gives you the performance you need, Mildred. If you think it is expensive to hire a professional, wait until you hire a complete amateur!

LG Dave is on the right track. Reduce friction. Every elbow has drag, cutting your flow. Use long sweep elbows wherever possible. Have the pump inlet straight for a foot before the pump so the flow can get laminar, not turbulent. Make sure the inlet is not producing a whirlpool, which will introduce air turbulence into the pump.