As someone else said, use a variable frequency drive. VFDs are used throughout commercial and industrial installations and control the speed of electric motors.
Someone wrote above that motors don’t like running at anything but their rated voltage. This is a gross inaccuracy since VFDs vary the voltage and the frequency to control the the speed of the motor often from zero RPM (holding a conveyer belt from rolling for example) to 60Hz or 100%.
I probably have a 1HP 240V VFD sitting in my shop somewhere. You can control it via the keypad or use a small potentiometer to vary the speed. You should be able to run the motor from a standstill to 100% without a problem.
Pumps are rated not only in power but also in flow and pressure. A 1 HP pump designed to circulate high flow at low head is not the same as a 1 HP pump designed to circulate a smaller flow at high pressure.
If you have a pump which is too powerful and you want to lower the pressure and flow rate you can easily put a bypass valve which connects the output back to the input and adjust the pressure/flow by adjusting this valve. It is a waste of energy but simpler than changing the pump and it allows a full range of adjustment.
I’m not quite following this. You used to have 1 solar heater with a 3/4 HP pump. This worked well. Then - you added a second solar heater, connected in parallel with the first, right? You also replaced the pump with a 1 HP model. So you now have a 1 HP pump, the outflow is then split and run through separate solar heaters, in parallel, and then the flow is merged prior to entering the pool? The end result is that the flow into the pool is still to fast. Is that about right?
If the above is correct, and you simply want to slow the flow of water, couldn’t you add a return loop. Essentially, instead of splitting the outflow 2 ways to go into the solar heaters, you split the outflow 3 ways, and have the 3rd line return to the pump inflow. This way, the pump still operates as intended, it’s just that roughly 1/3 of the water stays in a loop returning to the pump, while 2/3 of the water goes to the heaters and out to the pool.
Also - this might be a very silly question - but do you still have the original 3/4 HP pump?
Maybe the problem is not the power of the pump as much as the configuration of the piping. Maybe a different configuration would prevent this problem.
By if you just want lower flow rate all you need to do is restrict the flow, which can be as easy as a valve, or even a washer inserted at a union.
A “dimmer” will not work as intended. A Variable Frquency Drive is overkill. Rather than just try solutions you don’t understand I would advise analysing the problem. Again, it may just be a question of directing the flow differently.
a dimmer will not work because it will only decrease the voltage. An Ac motor speed is a function of cycles, number of poles, and slip. Decreasing the voltage will only increase the slip a small amount and increase the heat a large amount.
If you plug a 240 VAC motor into 110 VAC you will be buying a new motor.
Two cheap solutions are
put a valve on the pump discharge. But be aware that as you close the valve the motor amps will normally increase. so use an amp-prob while setting the flow rate.
Put a “T” in the discharge line one side going to the heater and pool the other side going through a valve back to a “T” in the pump suction.
Absolutely incorrect, at least for a centrifugal pump. The motor load is proportional to the flow. As the flow decreases, so does the motor load. When the pump is dead-headed the motor load is at a minimum. You can calculate brake horsepower (BHP) by:
(Flow in gpm * head in feet * specific gravity of liquid)/(3960 * efficiency)
Thanks for everyone’s answers. I am slowly working through this problem.
As for the post above, are you saying that I can divert the pump output directly into the input without going into the pool? And this will not cause problems for the pump? I currently have a T that bypasses the solar heaters but it does not bypass the pool.
Also, I sold by old pump. It was old and leaking. As for efficiency, I can only say from my research that pump efficiency has increased in recent years. They now pump more water using less current.
No, that won’t cause problems for the pump, but it will cause a problem for your turnover rate. Keep it the way it is now - you want to reduce flow through the heater, not the filter.
And if you have a tee that bypasses the solar heaters, then just put two globe valves on the outlet sides of the tee and use that to modulate the amount of water that passes through the heaters and the amount that goes directly to the pool. Seems to me that the solution is that simple.
Right on!
So that won’t increase the pressure on the pump and damage it?
Are you saying it is possible to completely shut off the outflow from the pump without causing any harm?
You should not let the pump run for an extended length of time with the outflow cut off (dead headed). A pump operates on a pressure/flow curve. You could google a representative one up. As the flow decreases, the total developed head (TDH) of the pump increases. Each pump, motor, and impeller combination will have its own characteristic curve.
In any system I design, I either design it for the dead head pressure of the pump, plus the net positive suction head (NPSH) or I put in safety relief valves. Your system may not be that way, and valves, pipes, and fittings can overpressurize and burst.
In the second place you can run too far to the left on the pump curve. This causes a loss of efficiency, and this loss of efficiency goes primarily into cavitation and tearing your pump apart. You can dead head a pump for some minutes, but not for hours. Without seeing the pump curve it is impossible to tell what your minimum flow rate should be, but you can usually run to 50% of the design flow, given that the design flow is somewhere neare the best efficiency point (BEP).
The pressure regulating valve combination previously described will work fine. Switching the impeller for a smaller one would work as well. I don’t know what a 1 HP VFD would cost, but I was just quoted $100,000 for a 450 HP VFD, and there’s almost no economy of scale on these things (in fact, the larger ones cost slightly more per HP), so I’d figure a couple hundred bucks anyway.
But as many people have already said, more flow should be better. You may need to study the system a little more before acting. If the problem is debris settling on the bottom, can’t you direct the return water to minimize it?
Not absolutely incorrect. It all depends on the operational curve of the pump. I have seen pumps trip the motor on over load when dead heading. Most will decrease if the mass rate of flow will decrease, some will not.