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Old 18-02-2016, 12:29   #1
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Shurflo Pressure Switch Failure (2nd in two years)

Hi Everyone,
We have a Shurflo Aqua-king II 4gm pump for our fresh water. In 2014, the pressure switch started flaking out and and ultimately stopped working in the middle of a cruise.

It was not a matter of adjusting the pressure set screw. I know about that. The little cheap plastic microswitch they use just failed (validated out of circuit with a meter). Shurflo sent me another pump. I figured I'd keep the old one as a spare because - what are the chances of that exact same switch failing in another pump?

Well here it is in 2016 and I'm washing dishes to a suddenly silent pump. Swearing a lot, I took this pressure transducer apart and sure enough - anther bad cheap plastic microswitch. If I click it a few times it works... intermittently for a few times and then just dies again.

Has anyone else had such similar luck with these? Any recommendations for a more reliable unit?

Thanks all
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Old 20-02-2016, 12:12   #2
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Re: Shurflo Pressure Switch Failure (2nd in two years)

No particular recommendations on a better pump, but 2 thoughts:

1. The microswitches are readily available, so you should be able to stock a few replacements for only a few bucks each.

2. If the full pump current goes through the microswitch (you can tell with an ammeter) then you might consider putting a capacitor across the switch. An automotive ignition capacitor would be a good choice. This will reduce the arcing inside the switch and likely make them last considerably longer. Take a bad switch apart and if the contacts are fried, this will help a lot.
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Old 20-02-2016, 14:07   #3
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Re: Shurflo Pressure Switch Failure (2nd in two years)

One thing that helps keep pressure pumps from failing prematurely is having an accumulator somewhere after the pump. If the pump is being used as the pressure regulator with no accumulator then the switch has to activate hundreds of times during each use. If you do have an accumulator it may have lost its air pressure charge.

If you have no accumulator and do not want to install one look into the more expensive variable speed pumps. These do not have a click type switch and are designed for boats without accumulators.
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Old 20-02-2016, 16:20   #4
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Re: Shurflo Pressure Switch Failure (2nd in two years)

The advice about spare switches is the best if you want to use a diaphragm pump. Also the advice about an accumulator. The switches are on Ebay and maybe Amazon. If you want a reliable switch, buy a switch for a shallow well pump. I use a shallow well pump for my water pressure and it's good for about 20 years and rebuildible.
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Old 20-02-2016, 16:32   #5
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Re: Shurflo Pressure Switch Failure (2nd in two years)

Thanks for the replies everyone. This has been a learning experience. The issue with these pumps is that they use a tiny microswitch to actually switch the pump motor directly - not through a relay. Yes, an accumulator will help, but the fact remains that they are using these switches way outside of their design spec.

I did an autopsy on the switch and sure enough - the contacts inside show lots of evidence of arcing. I'm surprised it worked as long as it did.

I'm doing several things:
1. Installing a Relay. The pressure switch will only need to energize a 130mA coil now instead of a 20A motor. The relay will energize the motor (well within it's design limit).
2. Installing a small accumulator.
3. Ordering 10 spare microswitches.

I think I'm covered
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Old 27-02-2016, 12:16   #6
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Re: Shurflo Pressure Switch Failure (2nd in two years)

Just to give conclusion to the story, I did put a relay into the switching circuit and add a small accumulator. It's working perfectly. Here's a description of the project with photos:
Argon Voyages: Water, Water Everywhere. But I can't flush

-bd
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