Pumps - Controlling the Flow (OUTPUT)

After some differing comments by hydrojeff I did some searching. I found a lot of technical info that was hard to read and understand.

From what I have read, you can control a centrifugal (C) pump in 3 main ways.

1. From the Input side - Big Risk of cavitation so only very knowledgeable techs should do it.

2. A bypass tube - here you set up a channel from the output back to the suction side. A very good method if you are handy.

3. Restricting the output side - From what I have read you can do this. I cannot find too much on the effects on the pump. I have found that a pump will heat up and its life shortened when the restriction is extreme. However, I have not found basic info stating an minor increase in Temperature with a small restriction.

4. Another way to control the pump is from the power side. Put in less power and the impeller will turn slower. Hence, a slower flow. I am going to find out if a "dimmer" switch can be used on our pumps.

Anyone with knowledge on this topic PLEASE jump in. Apparently, I really don't know what I am talking about.

 

sorry i did not mean to make you go and do all this research,it all depends on pump curve,and what the pump was designed for, you can not run a dimmer style switch on a pump because pumps rely on frequency not voltage to run you can lower the AC voltage and frequency then you will lower the speed of the pump, these (dimmers) for pumps are call VFDs...... P.S. there is a lot we all can learn just trying my best to help when i can i hope there is no hard feelings over this!!!!P.S.S you could run a dimmer on a DC pump

 

No. Thank you. I enjoy reading new things. I wish I could have found some rock solid answers but I have not. YET. ;D

I would never have hard feelings when learning. Then - I'd be a true imbecile.

Do they make a "dimmer" that uses some sort of in line resistor?

 

please don't put a dimmer on a motor. ( unless it's designed for motors). you can cause a fire.

How much are you trying to restrict? Can you get a smaller pump? Generally just restricting the output will have limited effect on a pump.

Keep im mind, that from the output of the pump. Every foot of pipe/tubing you have, is slowing down the water ( called head pressure). So, if your pump is on the ground and the return is in the tank 3 or 4 feet up, you are restricting the water.

Unless you are trying to restrict a 1000 gph down to 2 gph.. I would not take the time do a loop back. just get a size that is close and all should be good.

Also keep in mind. In addition to to every foot of pipe/tube each 90 degree turn adds 1 foot of head pressure

 

What about controlling the pump speed with a router speed control:
Router Speed Control - Rockler Woodworking Tools

 

Just put a valve after the output and regulate it like that. Most pump will use less power when dialed back.

 

Don't throttle the inlet. You starve the pump.

No point. The pump will only consume the power it takes to move the water. Bypassing some flow back to the suction will give you the final output you want, but you will always be moving 100% flow and power consumption.

A centrifical pump should never be dead headed for too long. Zero flow. The friction with the impeller will heat the water. You always want enough movement to prevent heating. 10%-20%. With you trying to throttle flow, you will not get to this point. You could get to 25%, but then you are just using a pump 4 times bigger than you need.

You will only consume the power it takes to move the water you are moving.

The only thing to consider is what type of valve. Ball valves are really only good for isolation. They do a poor job of throttling. If you find a point that works great, but there are better. Their advantage is that when open, they give 100% flow.

Gate valves are much better for throtteling. They too offer almost zero restriction when open 100%.

Bad idea. Lot more involved. Much easier with a mechanical solution.

 

Only way to safely cut a pumps flow back is either through the by pass and or a single flow control valve or a globe or gate valve , Cutting the motor speed by decreasing the voltage will only cause the pump to draw more amps and this will burn the motor out . Same way a simple ceiling fan's rheostat control switch starts on High and will only allow so many speeds for a motor with a armature designed for speed control . Many people tried to use a simple light dimmer switch and burned out fans or switched would buzz and smoke.. Never restrict the voltage to slow a single speed motor ..Also never ever restrict the inlet flow to a pump it will suck the seals and or create cavatation in the the impeller housing and the boiling water will do the rest. ..

 

We use do do this in college in my analog circuits lab. Put a capacitor across it and when that current spiked it made an awesome little firecracker! followed by a sweet smoke bomb! hahah anyway enough reminiscing... So yeah dont restrict the voltage its a bad idea!

 

Globe valves have very good flow control characteristics. Much more linear adjustments than gates. However, they are very restrictive valves compared to gates and balls.