Way to Reduce Pump Speed?

[waterfixer]

Recently I've been searching for a way to reduce the rate at which the pressure tank fills in order to prevent this well from running dry. I would like to slow the pump down with a variable AC motor speed controller such as the kind used for power equipment, but am not sure if this type of control is compatible with a well pump. This is the SCR type of motor speed controller used for fans, routers and other high current appliances. Would it cause any harm to try it out?

Alternately would connecting the pump to a variac be a viable way to slow it down and reduce the refill rate of the pressure tank? The only other idea I have is to install a shutoff valve on the water supply line from the pump, but am not sure if this is a good idea either.

 

[GReynolds929]

You could just use a ball valve to throttle the pump down to the needed flow rate. Cheap and won't damage the pump.

 

[Sponsor]

 

[Reach4]

You can use a Dole valve to reduce the flow. Is this a submersible (down the well) pump?

 

[waterfixer]

Thanks for the advice. I like the idea of using a valve on the supply side, but am concerned that it might cause the back pressure to increase too far on these old house pipes. I'm not sure yet what kind of pump this well has, but it's very audible when running so I'd guess it's the above ground type. It's not visible from the pressure tank access door, so I'll try to find out from the builder.

If it were possible to reduce the rate of water being supplied by reducing the current and speed of the pump motor, it would make less pressure but also help save energy. I'd prefer to slowly fill a resevoir tank over the course of hours instead of minutes, and lower the cost of running the pump. A variable SCR motor speed controller for 220v seems to be the least costly option, but I'm not sure if it would work or cause some kind of damage. Do well pumps in general use the same kind of AC motor that can be reduced in speed with this type of control?

 

[Fitter30]

Use a globe valve in the bottom out the top or a circuit setter one size smaller than pipe size is more precise than ball valve. Use a reducing coupling to decrease pipe size. There isn't a good way to vary the rpm with a permanent split capacitor motor.

 

[Valveman]

If it were possible to reduce the rate of water being supplied by reducing the current and speed of the pump motor, it would make less pressure but also help save energy.

NO! Varying the pump speed DOES NOT SAVE ENERGY! Anytime you reduce the speed pf a pump it uses more energy per gallon to pump the water. Yes, the amps to spin the pump and motor decrease, which is how they trick you into paying more. You can see the amps drop, and think it is saving energy when just the opposite is true. Many things about pumps are counter intuitive and they just let you think intuitively and keep paying through the nose for replacement pump after replacement pump. Oh, and the pulsing DC power, trying to simulate a smooth sinusoidal AC wave, is one of the many things a variable speed controller does to shorten the life of the pump/motor and cause you to purchase a new one often.

What else pump manufacturers won't tell you is that the amps drop the same way when using a valve to throttle the output of the pump. The pump stays at full speed, but the reduced flow from just a valve can make the amps drop 30% to 60%, same as a VFD or variable speed pump. A valve is also not saving energy, but can reduce amps the same and keep the well from being pumped dry while slowing filling a storage tank. Plus, throttling with a valve can make pumps last much longer than normal, also counter intuitive.

But it sounds like you may just have a regular pressure tank and not a big storage or cistern tank? If so, even filling a large pressure tank at the end of a water use cycle in the house can cause the well to be pumped dry.

A Cycle Stop Valve is a much better way to accomplish what you just said, and has been replacing variable speed pumps for well over 30 years so far.

With a low producing well, you may need a cistern like in the second picture if you don't already have one.

 

[waterfixer]

I appreciate all the information. The tank is just a regular pressure tank, and for years now this well has been running dry in the summer making it impossible to irrigate. I had never known much about well pump systems, but got the notion it must be pumping water out too fast. Thank you all for sharing. The knowledge to add a basic valve to throttle the pump is most helpful, and I'm glad to know it will also help reduce the energy usage.

 

[Valveman]

It only pumps water out as fast as you are using it. A storage or cistern tank to store a days worth of irrigation water can then slowly refill while not pumping the well dry.

 

[Reach4]

Rather than throttling, better might be to install a device that shuts down the pump for a while if the well runs out of water.

 

[Valveman]

Rather than throttling, better might be to install a device that shuts down the pump for a while if the well runs out of water.

Or both.