How far can you throttle down the discharge on a solar hot water circulating pump ?

[ilbebauck]

Im wanting to install this Pump for my open type solar hot water heater (Florida) :

I want to be able to adjust the water flow rate thru the solar collector when im setting up the system, and need to know how far I can throttle down the water flow discharge without adversely affecting the Pump/Motor ? The Pump Specs maxes the head out at 9 ' but my system will only have 4' total , so I want to put in an adjustable flow control valve right after the pump. Thanks for helping.

[Steve]

Watch your current draw... not a real good idea to excede that unless you want to burn up the pump motor..... also be carefull you don't cause the pump to cavitate.... thats not a good thing either.

[ilbebauck]

So then, are you saying that I can throttle down the flow so long as i dont exceed the amp draw of the pumps motor ? Thanks.

[Steve]

So then, are you saying that I can throttle down the flow so long as i dont exceed the amp draw of the pumps motor ? Thanks.

Or cause the pump to cavitate.... cavitation will cause the pump to eat itself from the inside out, an you won't even know about the damage until its too late.

[ilbebauck]

.

Is there a way to detect that its cavitating ? Can you readily hear it ? Also, how far downstream of the pump should the flow control valve be located ?

[Stormin Mormon]

From my fire dept days, cavitation is when the pump supply is restricted. It's a very real concern. However, restricting the discharge is not likely to cavitate. Might over amp, or over heat.

[Grumpy]

Why don't you put by pass on it then you can throttle all you want and beside that is what you should have to start with

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[ilbebauck]

Here is what the Rep. at Taco Pump just said : ' Any of our circs can operate when throttled right back. All of the 00 circs are impedance protected so will protect the motor even in a locked rotor situation.' So, it seems they can be throttled back pretty far without harm to the pump/motor.

[Real Pisser]

>

The spec sheet on this pump shows the cartridge impeller, and it looks like a simple centrifugal pump. These pumps typically draw the most current when they are moving the maximum volume of water they are designed to pump per minute. Restricting the discharge at the **outlet** on these pumps causes the motor to actually have less of a load on them than when pumping the full flow. Cavitation will result only when the suction intake of the pump is restricted.

Grumpy's (Tony) suggestion of a bypass around the collector sounds good too, but will not reduce the amperage the motor draws in bypass mode.

[ilbebauck]

.

Thanks.

[Suka Midak]

>

BS on this one. Throttling down the output will cause the current draw to be less.

[Suka Midak]

>>

AMEN! Give this man a cigar!

[Reno]

"Grumpy" wrote in news:hi889t$26g4$ [e-mail]:

The answer to your question is that you can throttle it down a lot without harming the pump. It needs just enough flow to lubricate and cool the impellor and bearings. It depends on how long you will run it throttled which isn't clear from your post. If the time is short then you could stop the flow entirely for, say 3 to 5 minutes. If the setup is permanent then you could throttle it to 1/4 or 1/3 of the peak flow with no problems. Some pumps could be throttled to 10% of their peak flows.

Your post raises some questions beyond what you asked such as;

- a system with only 4' of head seems very low to allow for vertical lift plus system head losses.

- a pump that makes only 9' of head is very low.

- throttling makes noise

- throttling releases air from the water which increases bubble problems.