Should I try to soft start a pump?

[Alternety]

I am going to install a 25 GPM centrifugal pressure pump (Goulds 25GBS1511J4) for house pressure. It is going to run at 240VAC. It will be run at 40/60. The pump has a start capacitor in the motor. There are two Amtrol tanks (either WX-302 or WX-350).

I have been wondering if there is any merit to trying to provide a soft start mechanism to the pump. The placement of the phase shift capacitor seems to contraindicate it. And I really have no idea if it will help the pump lifetime.

What do you guys think. Please don't try to fool with the pump or tank types. Done deal.

 

[Valveman]

There is really no way to soft start a single phase motor. Soft starting won't help anything anyway. It is not so much a "hard start" that will hurt the pump, but the number of times it starts.

You would think those two big tanks would be enough to reduce the cycling. However, a WX302 only holds about 25 gallons of water, 50 gallons for two of them. With a 25 GPM pump, while using 12 GPM continuously, the pump would still cycle ever 8 minutes, which can add up to 221 cycles per day. Those large numbers of starts per day is what will shorten the life of the pump/motor. It doesn't matter if they are "soft starts" or not.

You can still add a CSV before the tank(s), which will completely eliminate cycling for those long term uses of water. But then you would realize you didn't need those big tanks, which are very expensive. You could have saved the money on the tanks to use on a nice vacation or something.

 

[Sponsor]

 

[DonL]

Soft start systems are normally made for Transformers, That feed heavy Loads.

The Motor needs a boost, That is why it has a capacitor and Start winding.

When Transformers charge large caps on the secondary, Softstart is great.

For a pump motor, not so much, as Valveman was saying.

A CSV would be a better option, and keep you from smoking your motor, by modifying the phase / start current.


Good Luck.

 

[LLigetfa]

I have been wondering if there is any merit to trying to provide a soft start mechanism to the pump...

Explain how you think a soft start is needed or beneficial. I cannot see where spending more time on the start windings would do any good. Also, the bearings in the pump run on a film of water so you want them up to speed as fast as possible.

Centrifugal pumps are not solid displacement. Their volutes allow a certain amount of slip at lower RPM so they are inherently soft start in a sense.

 

[Reach4]

I am going to install a 25 GPM centrifugal pressure pump (Goulds 25GBS1511J4) for house pressure. It is going to run at 240VAC. It will be run at 40/60. The pump has a start capacitor in the motor. There are two Amtrol tanks (either WX-302 or WX-350).

I found some curves that you might find of interest.

http://en.wikipedia.org/wiki/NPSH explain NPSHR.

 

[DonL]

Just running that Motor on 240 is going to be a big help.

Nice move on your part.

LLigetfa hit the nail on the head.

 

[Texas Wellman]

Not in the pump he is using. They use regular sealed bearings that are greased.

Also, the bearings in the pump run on a film of water so you want them up to speed as fast as possible.

Centrifugal pumps are not solid displacement. Their volutes allow a certain amount of slip at lower RPM so they are inherently soft start in a sense.

 

[Valveman]

Not in the pump he is using. They use regular sealed bearings that are greased.

And very little grease I think.

 

[Alternety]

Sorry to take so long to get back here. I am not getting alerts when someone posts to a thread. If I look at threads I am following, there are none. I don't know what I am doing wrong. I have gone back and run through all my settings a couple of times.

I really did not think it was useful, but I wanted to get some expert input. The "phase shift capacitor" I mentioned is the starter cap mentioned in the replies. It provides phase shifted AC to the starter winding. One could actually provide a different starting process; but not useful. The bearings in the pump motor are sealed and the ones in the centrifugal portion are, I believe water immersed.

Now the big item - I have seriously over sized the pump. The 7 vane would have been a better choice. I seem to have made a mistake in converting ft of head to psi. That is very annoying since I already have the pump. I hate it when that happens. It is certainly going to increase the number of starts under some conditions. For normal household demands it is probably not a huge difference. When watering the yard; probably excessive cycling. It is (was) sized to provide a reasonable supply of water to fight a fire. I live in a forest. One that gets very dry every year. There have been two fires within 1/2 mile of me over that last three years. And a third about 10 years ago within 2 miles. And an earlier one (time unknown) that is clearly evident if I walk around parts of my property. Three of those attributable to deeply human stupidity.

 

[DonL]

So how many degrees of phase shift do you expect that Cap to give You ?

Even if you change the phase, the output of the cap is still 60HZ.

If you do not have a 180 degree shift on the motor winding, it will heat up. Both Start and Run winding.

You should not play with electricity without the proper PPE.

 

[Valveman]

You seem to be ignoring the one good way to solve this problem. The CSV was designed to allow you to install as large a pump as you may need, like for fire protection, and still be able to use that big pump for small demands without cyclgin the pump to death.

You can still add a CSV before the tank(s), which will completely eliminate cycling for those long term uses of water. But then you would realize you didn't need those big tanks, which are very expensive. You could have saved the money on the tanks to use on a nice vacation or something.

 

[DonL]

You seem to be ignoring the one good way to solve this problem. The CSV was designed to allow you to install as large a pump as you may need, like for fire protection, and still be able to use that big pump for small demands without cyclgin the pump to death.

That is what I would do.

Or connect the cap backward to change the Phase. lol


You invented a new word, I like it.

 

[Alternety]

Well it has been a long time since the motors course, but:

The motor in the pump has an internally located cap which is disconnected as the motor comes up to speed. When a single phase induction motor is at rest there are no magnetic fields being created. Applying power to the primary winding will not cause the motor to rotate because while there is not a field from the main coil, there is no field to push against. The solution is to place a smaller lighter winding in the motor. It is placed in series with a capacitor and (in our example) a centrifugal switch that takes the cap and auxiliary coil out the circuit when the motor comes up to speed. Once running at speed the assorted fields take care of themselves.

The combination of the starter coil characteristics (resistance and inductance) are matched to a capacitor with a calculated value that will provide a resonant circuit with a 90 degree phase shift in the current flowing through the secondary winding. At this point AC is being provided to both coils. But now, the phase difference between the magnetic fields in the two windings will supply the electromagnetic fields required to provide the primary something to push on. As the motor achieves sufficient speed, the cap and aux winding is disconnected. This process provides significant torque at start-up. A bit of a visual for you. There are other ways to do this.



Fig 7(a) Circuit diagram of a capacitor-star motor


There are a number of variants in the design of single phase AC motors. This one is pretty common for this range of power output. I note in passing, one should be thoughtful in flinging missiles about while standing in a glass enclosure.

As an after thought. When I was going to school, a design of mine replaced the professors approach on a space probe that was launched. Sorta like rocket science.

 

[LLigetfa]

Sorta like rocket science.

Oh, so you're like a rocket scientist too?

 

[LLigetfa]

You seem to be ignoring the one good way to solve this problem. The CSV...

Depending on how the CSV is adjusted, it could start the pump against a closed valve which in turn would soften the start.

 

[Alternety]

Just a side comment on the CSV. This is an inside pump that is heard throughout the house when running. It is not clear that I would prefer constant noise to intermittent noise. I am hoping to reduce this noise. The original pump was supposed to sit on noise reducing mounts. I gave the plumber the materials and when I came back it was attached directly to the concrete. I am going to see if I can find a secure anti-vibration coupler to the piping as well. I seem to remember seeing such things. A stainless steel mesh over a flexible material.

 

[Craigpump]

A piece of Pex between the pump and piping will help reduce the noise trasmitted to the pipes. Years ago I built a plywood enclosure lined with jute carpet padding to go over the jet pump on an Air Rader Radon system to cut down on the noise. The customer loved it!

 

[Valveman]

A submersible pump inside the storage tank would have been really quiet.

Isolate the pump with a piece of flexible pipe and cover the pump with an insulated box the way Craigpump says. Just make sure you allow for the air flow that kind of motor needs to stay cool.

The backpressure from a CSV usually makes a pump like that more quite. But it will run for longer periods of time. Personally I prefer a steady hum to a couple of minutes of “roaring” followed by a couple of minutes of quite, which keeps repeating itself over and over. But knowing how that continual cycling on and off is destroying the pump is probably more annoying to me than the actual noise.

 

[Reach4]

Well it has been a long time since the motors course, but:

The motor in the pump has an internally located cap which is disconnected as the motor comes up to speed.

While a motor could work that way, I am pretty sure that is not how the Goulds pump motor. works. I believe the 2-wire Goulds CentriPro motors are PSC motors, and they are proud of it. http://en.wikipedia.org/wiki/AC_motor

There are 2-wire motors with a switch in the motor, but most of those are split-phase.

 

[DonL]

I would like to see the Soft start circuit design that alternety plans on using that will work better than the motor manufactures design.


I new EE job may be available.