How to control the flow rate in a 3-phase pump?

[Ed from NY]

Hi, I have a Graymills IMV-100 1HP (50 GPM) coolant pump. I can run it full blast by just wiring it 3-phase and control on/off with a relay -- that would be fine, but... I was wondering if there is a cheap way to control the flow rate with dial of sorts.

Thanks!

[awemawson]

You need an appropriately rated three phase in three phase out inverter wired to a twiddle pot. OR it may be possible to choke the pump flow with a suitable gate valve.

[mactec54]

Ed from NY

Not that cheap but quite easy, because you have a 3phase motor, you can use a VFD drive to control the motor speed

[Geof]

If it is a centrifugal pump controlling the flow rate by controlling the motor speed is sometimes not so effective because the pressure drops off rapidly as the speed is reduced.

But if it is centrifugal it is more or less impossible to overload by choking the flow so just use a valve. To be picky it should not be a gate valve because these are intended to be fully closed or fully open, similar to ball valves. Use the other type, a poppet (?) valve. Or a big needle valve.

[Bubba]

IIRC, that is a centrifugal pump. Therefore, the flow is proportional to the rpm, the head (pressure) is proportional to the rpm(squared), and the power requirement proportional to the rpm (cubed). Yes, you can also choke it down with a valve on the discharge, but you do not want to run against a dead head (zero flow) for an extended period of time as this will cause heating in the pump.
A VFD is the way to go and is also what they are doing in a lot of industrial situations now.

[Ed from NY]

Hmmm it sounds like it would be something like this

GS1-21P0 Products

A bit on the expensive side, but it does have a knob and it ia 1hp. Sigh! I was hoping to grab a dimmer at homedepot :lol: -- well not really

[Geof]

A VFD controlling a coolant pump seems a bit of overkill to me. Get a cheap valve and just throttle the flow with this. Coolant pumps operate with the pump fully immersed so you are never going to overheat anything running the pump with the flow completely blocked.

[UUU]

Fit a branch in the flow pipe and route one side through a valve back to the tank. When you open the valve nearly all the flow goes straight back to the tank. As you close the valve more of the flow goes to the work. But the pump is always running at full flow, so there's no overheating issue.

[underthetire]

Originally Posted by Geof A VFD controlling a coolant pump seems a bit of overkill to me. Get a cheap valve and just throttle the flow with this. Coolant pumps operate with the pump fully immersed so you are never going to overheat anything running the pump with the flow completely blocked.

Never seen a 3phase pump "fully" immersed. Just the fountain type pumps. The VFd is a nice way to go, and that unit is super cheap Ed posted. Gate valves work, to a point. If you get them closed too much, the pumps will start cavitation and make a lot of noise and vibration, and can cause heat in the coolant. Hell, a 3 phase 1HP rated contactor is 80-90 bucks alone, not much more to go to the VFD.

[Geof]

The pump is fully immersed, the motor sits above the tank.

[Ed from NY]

I was planing to hook it up today but did not get to it -- need to run a bit of wiring and change to a larger coolant tank. We will see how much splashing we get. The one thing with the gate valve is that, as I have it set up now, I have to open the door in order to adjust it, which depending on the flow and where the splashing is going means waiting till the cycle is complete... I could change the plumbing, but then... well, we will see.

[Ed from NY]

I hooked it up today and the pump at full throttle is just what the doctor ordered. No need to reduce the flow, though you do need to turn it off before opening the door... or else