POOL PUMP MOTOR CONTROL

[filterengineer]

Hi Guys,

I got a Pentair Wwhisperflo in ground pool pump for free from a friend and mounted it up to my above ground pool. It filters great and has a pretty good turnover rate on the water but there is one issue, the motor is too powerful when it comes to hooking up the vacuum. Once the vacuum is hooked up, the pump exceeds the flow capacity of the vacuum and it begins to suck air through the pump basket lid. I'm wondering if there is a safe way to knock back the speed on the motor. I'm writing up this thread while I'm at work so I don't have the nameplate info from the motor in front of me, but I'll update the thread with that info once I get home this evening. It is connected to a 120V residential outlet though. Any ideas you guys have would be great, I've been investigating a VFD but I really only need two speeds out it, not "infinitely variable" speed. Thanks Guys!

 

[jraef]

Most likely this is a centrifugal pump. As such, you can get the necessary effect by simply restricting flow directly, ie with a valve or even just put a fitting in line somewhere that reduces the orifice, selected by trial and error.

There is no practical way of varying the speed of a standard 120V motor. SOME more modern pool pump motors are now coming with a VFD built into the motor itself, ie the motor is actually 230V 3 phase and they use the VFD along with a "voltage doubler" so that it can accept 120V single phase. But I doubt anyone would "give away" one of those, they are very very expensive and a hot item on places like eBay or Craigslist. It's more likely your friend bought one of those and gave you his older fixed speed version.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

What Jeff said.
Don't try to change the speed of the motor, restrict the flow.
With the flow restricted, the motor will use less energy also.
I have seen industrial irrigation pumps that would burn out if they were allowed to pump with too little back pressure.
When we installed them, we used a valve on the discharge to limit the flow to a safe level.
We would use an ammeter to monitor the current while we throttled down the discharge.
Then we would either wire the valve handle in place or remove the valve handle.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[filterengineer]

ok, sounds better than buying electronics to me. only question now would be which end of the system would be better to have the flow control valve, suction or pressure side?

 

[ScottyUK]

Suction side will cause cavitation. Restrict flow on the discharge side.

 

[jraef]

Bingo


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[itsmoked]

Yep, always the discharge. You can throttle it down to about 5% with no issues.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[OperaHouse]

I have a hot tub and the impeller broke after 10 years. A lot of pumps are common to both pools and hot tubs. I found another impeller locally but it was a lower flow rate and rated for a lower hp motor. That was ok with me. So you might have the option to change the impeller. They spin on. Note: ebay has the cheapest price on seals. You can get a half dozen for the price of one locally.

 

[waross]

Another solution is to reduce the diameter of the impeller. This is usually more expensive than restricting the flow but has the advantage that no-one can change the setting of the throttling valve.
I once had an application where it was not feasible to throttle the flow. An order was given to have the diameter of the impeller reduced. Due to some mix-up, the thickness of the open face impeller was reduced instead of the diameter. That did reduce the flow but loss of flow due to cavitation was so frequent that the impeller was replaced with a new impeller, properly reduced in diameter.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[filterengineer]

Ok, thanks for all the help guys. I'm not too worried about anyone messing with a throttling valve since its for the pool at my house. what type of valve would work best for this application, My guess would be globe but I'm not sure I could get an 1-1/2" PVC globe valve for any reasonable price if they even exist.

 

[mcgyvr]

You can easily pick up a PVC gate valve in that size for fairly cheap (under $25-30). It will be much easier to dial in vs a ball valve.. Not that precision should really be an issue there..

 

[waross]

The OP mentioned a GLOBE valve, not a BALL valve.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

A globe valve would half to be the last-valve-on-earth before considering it.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[filterengineer]

itsmoked, why would that be case? I thought most globe valve were specifically designed for throttling purposes, no?

 

[itsmoked]

I think they are primarily made to be restrictive with their torturous flow paths. Installing a globe valve and leaving it wide-open would probably be enough restriction for your application. They often have a rubber seat that will fail with time. They're also directional.

You say you want reduce flow when vacuuming? If you don't want to also reduce flow during normal pool operations then put in a tee with a solenoid valve in one leg you shut-off when doing the maintenance.

BTW I'm not sure what above ground pools have for suction ports but I hope you've checked them for being impossible to pin a swimmer. Seems to have been a lot of those sad accidents lately.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Compositepro]

The suction power at the vacuum can better be regulated by cutting a hole in the vacuum hose where it connects to the pass-through the pool wall. My pool came with a tee to place in the hose at this point, which also had a gauge to indicate when the flow was correct.