I pump lawn irrigation water from a lake, using a Sta-Rite 2 hp pump with a Sta-Rite 40 gal. bladder tank. The system was installed in 1999. The pickup in the lake is about 30 ft horizontal, 6-8 ft vertical, from the pump. It has a stainer, no filter, and a check valve. Both have been replaced as needed, most recently a week ago due to check valve failure and crud on the strainer.

Usually everything works as expected. However, sometimes the water stops and I find that the pressure switch contacts are closed (making contact) but the pump is not running.

To get the pump running again, I use an insulated screwdriver to manually pop the contacts open. The pump then starts and everything works. If that happens often, I replace the pressure switch. That usually fixes the problem for 1-2 years.

Recently, I replaced the pressure switch with a new one (20-40), and the problem occurred the first night that the sprinklers should have run.

What could cause such a failure?

Thanks for your help.

Best guess. Pressure switch isn't rated for the load. Can you post a model # and/or link for the pressure switch?

Would you happen to know the FLA (Full load amps) of the motor?

Motor is 240 VAC 1 phase 2HP? Pressure switch contacts are rated for?

If you examine the contacts of the pressure switch, they are probably pitted and dark.

Where I'm heading is that you probably need to add a properly rated single phase motor starter.

Let's see what you come up with?

For a brief description of a starter, see here: Magnetic Motor Starters and Contactors Sales - Motor Starter Sale!

Usually 3 phase motors have an enclosure with a disconnect, a starter, on/off/auto switches, 3 phase protection and an electronic or magnetic starter.

A single phase 2 HP motor will be a good candidate for a motor starter.

Here is probably a candidate for your system. GE CR306K003 - NEMA Size 1...

You have to get the overloads separately. Electronic versions are available. The electronic ones have potentiometers to adjust the FLA of the starter.

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Originally Posted by KeepItSimpleStupid

best guess. Pressure switch isn't rated for the load. Can you post a model # and/or link for the pressure switch?

Would you happen to know the FLA (Full load amps) of the motor?

Motor is 240 VAC 1 phase 2HP? Pressure switch contacts are rated for?

If you examine the contacts of the pressure switch, they are probably pitted and dark.

Where I'm heading is that you probably need to add a properly rated single phase motor starter.

Let's see what you come up with?

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Thanks for the quick reply.

The pump is a Sta-Rite model DSGH-102L, 2 hp, 230 volt, single phase, Max Load Amps = 12.0.

The pressure switch is a ProPlumber purchased at Lowe's. The Lowe's number is 73924. The box and instruction give no ratings/specifications other than 20-40 PSI. The voltage across the switch's hot leads is about 220.

In the past, failures have been with old pressure switches where I assumed the contacts were pitted. This time the switch is new so should not be pitted.

Since the problem only occurs with the contacts closed, could the problem be the thermal overload on the pump motor? Otherwise, why would the motor fail to run when the contacts are closed?

I found these ratings for the switch which are at the maximum. water pump pressure switch 20/40,30/50,40/60 brand-new - eBay (item 280378735228 end time Aug-28-09 07:09:32 PDT)

Tampa, I would get a voltmeter and find out if you do/don't have current at the pump when the pump refuses to run. If you do have current, then it's a pump issue. If you don't have current, it's a switch issue.

You could actually have a bad winding and that makes more sense. In esscense it stops on a paricular winding and by you essentially starting and stopping it, your nudgeing it past the winding problem.

This usually happens on a commutated winding though. I could not find a manual to figure out what kind of motor it is.

The thermal would start automatically, I would think.

Thanks to KeepItSimpleStupid and jlisenbe for their suggestions. I will try to recreate the problem and check the voltage at the motor.

If the voltage is correct, would that mean that I need a new pump and motor, just the motor, or none of the above?

Hi Doug, Hello from Sarasota.
I used to work for Henry Gonzolazs Plumbing back in the 60's in Tampa.
You state,

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I will try to recreate the problem and check the voltage at the motor.

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However, jilsenbe isn't asking you to check the voltage,

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I would get a voltmeter and find out if you do/don't have current at the pump when the pump refuses to run.

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He's asking you to check the amperage or the load on the windings when the pump refuses to turn over and start.
To check current you will need a AMP-Probe or a Ammeter. Good luck, Tom

Actually, I just wanted him to see if the switch was operating properly to get electricity to the pump. In other words, just isolate the problem. If the pump has current (term used loosely), then you know the switch is OK. If the pump does not have current, and the points are closed, then the switch is the problem. If the switch is working properly and the pump is getting "juice", then Keep It Simple or Speedball or someone else will need to give advice on troubleshooting the pump.

Jilsenbe,
There's a lot of difference between voltage and current. Yiou asked him to check the current

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I would get a voltmeter and find out if you do/don't have current at the pump when the pump refuses to run.

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That's what through me off. Regards, Tom

You are correct. I did not choose my words carefully.