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Brand new water pump short cycling!


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I bought two very cheap automatic water pressure pumps on Lazada and installed one on my 1000 liter water tank to the house water system. Before installing the pump, I assumed that the small accumulator was filled with air rather than nitrogen. So I took both to my local garage with the very nice nitrogen filling system with very high accuracy. I removed the schrader valves from both accumulators and emptied them completely thinking that it was air going out. The garage tried to fill them with the nice nitrogen filling system but perhaps because the accumulators were too small, the nice system didn't work. So the mechanic used the standard filling valve which had the first mark on the gauge at 2 bar so it was very inaccurate. So I brought them home and used my 12 volt air compressor with a gauge on it and filled them to 1.5 bar with air. In the end, it was a failure because the short cycling was there on start up. I did expect a bit of short cycling because the accumulator is only 2 liters. But now I want to add another large accumulator somewhere in the discharge line but I find the prices are very high. Even more than the pump which was only 930 baht each. 

 

I have considered making my own accumulator out of 4" Schedule 40 or Schedule 80 PVC pipe about one meter tall  with a schedule 80 endcap and just fit valves on it so that when it gets water logged, I can easily drain out the water. This should be about 8 liters capacity. I just don't know if I can find those kind of materials easily or cheaply.

Has any of you DIY guys found a cheap and easy solution so that I don't burn up my two new pumps?

 

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14 minutes ago, Yellowtail said:

Install float switches

The float switches are already installed but they control the submersible pump that is in the 42 meter deep well. You can see the float switch in orange on top of the blue 1000 liter water tank. The small pump is the pump that provides water pressure to the house. That pump only turns on when someone opens a tap in the house. That is the pump that is short cycling when a tap is open. If there are three taps open the pump runs continuous and will stop when the three taps are closed.

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Sorry, I thought the pump was filling the tank. 

 

Are you sure it is the pump and not a leaky toilet or some-such?

 

You have two pump, why not try swapping them?

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18 minutes ago, Yellowtail said:

Sorry, I thought the pump was filling the tank. 

 

Are you sure it is the pump and not a leaky toilet or some-such?

 

You have two pump, why not try swapping them?

Both pumps are brand new. The accumulator is only 2 liters and the pump is 1 HP. It could be a bad bad pressure switch. I might try to swap them out and see what happens. I have decided in any case to build my own home made accumulator. I will take a 4 inch PVC pipe about one meter long and glue and round endcap on the top of the pipe. That pipe should hold about 8 liters of water. On the other end of the pipe, I will fit a reducer down to 1/2 inch and then fit a 1/2 inch Tee. On one side I will fit a 1/2 inch valve with a drain pipe and the other side a 1/2 inch valve and the connect to the pressure pipe on the discharge side of the pump. I will then fix with clamps to the concrete wall in a vertical position with the valves at the bottom and the round 4 inch end cap at the top. The idea is that the PVC pipe will have an air pocket that will compress the air when the pump is running and expand when the pressure drops. I know that eventually the pipe will get water logged as the compressed air will get absorbed by the water. But I will be able to hear when the pump starts to short cycle and when it does, I will close the water valve to the 1 meter tall accumulator and drain the water logged accumulator and then close the valve when the pipe is empty and then open the valve from the pump which will then start compressing the air again. I figure I can do this whole job for about 500 baht. 

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On 1/13/2021 at 5:23 PM, thaisail said:

Before installing the pump, I assumed that the small accumulator was filled with air rather than nitrogen.

It is usually best to try using the pump as supplied before making any changes.

 

One reason is that without that step you have no idea if it would have functioned in your system without the change.

 

A 100% nitrogen fill is extremely unlikely to function in any different way from a 79% nitrogen fill.

 

it is perfectly possible (probable) that the pressure you have installed into the small tank is different from the design pressure. It is likely that a different pressure will cause the pump to function differently, that difference may be what you want, but equally it may not.

 

Your suggested design of an external pressure chamber is functional and has been used in other systems. The refilling with air should only need to be an annual maintenance task if it’s big enough.

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1 hour ago, sometimewoodworker said:

It is usually best to try using the pump as supplied before making any changes.

 

One reason is that without that step you have no idea if it would have functioned in your system without the change.

 

A 100% nitrogen fill is extremely unlikely to function in any different way from a 79% nitrogen fill.

 

it is perfectly possible (probable) that the pressure you have installed into the small tank is different from the design pressure. It is likely that a different pressure will cause the pump to function differently, that difference may be what you want, but equally it may not.

 

Your suggested design of an external pressure chamber is functional and has been used in other systems. The refilling with air should only need to be an annual maintenance task if it’s big enough.

I agree! I should have fitted the pump first before making any modifications. I will order an accurate pressure gauge on Lazada to check the pressure in the bladder on the accumulator and set them for 1.5 bar. But it won't matter too much when I get my 8 liter DIY pressure pressure chamber fitted. I also will order a pressure gauge to fit on the new pressure chamber which will let me know if the pressure switch is cutting in and out at the correct pressure. This pump is fitted with a check valve on the water inlet side which is slamming shut each time the pump stops. Perhaps this shock wave from  the check valve is causing the contacts in pressure switch right next to the check valve to chatter. If the switch burns up from all the arcing caused by the chattering, I will fit an external pressure switch to control the pump from a location about one meter from the pump.

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1 hour ago, thaisail said:

I will order an accurate pressure gauge on Lazada to check the pressure in the bladder on the accumulator and set them for 1.5 bar.

Are you sure that that pressure is correct? 

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11 hours ago, sometimewoodworker said:

Are you sure that that pressure is correct? 

1.5 bar is the pre-charge pressure that is shown in the photo of the pump in the original posting.

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