Adding a flow switch to an electric pump...

Seems to be in perfect working order to be fair - very good pressure when running.

It was a woman selling it as her father had died and she was clearing his house out prior to sale.

Video in action:

garmcqui said:

Thanks all, some decent discussion here
In terms of protection for the pump, using a contactor etc, I’m inclined to think it’s overkill. I picked up the pump on eBay for £45! happy to be convinced!

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This is an excerpt fro 17th regs: 552.1.2 Every electric motor having a rating exceeding 0.37 kW shall be provided with control equipment incorporating means of protection against overload of the motor.
As you have it now is fine, however you are proposing to turn this into a fixed and automatic system, my experience says not to ignore the regs and advice.

The inrush for motors is very commonly described as 10 times their rated current, in practice the instantaneous surge for pumps is usually more than this as the impeller is being held static by the fluid. Relay contacts are not designed for that sort of work, I've replaced many 16A relays which have been destroyed by switching pumps much smaller than yours. I've also cleaned up after motors have overheated due to running at a higher current than designed and it's not pretty.

I'm only offering my as advice based on a number of years working in the controls environment [and making a lot of money repairing incorrectly fitted kit].

bernardgreen said:

Good point, with the water butts higher than the tap a centrifugal pump would allow some flow of water through the pump when the tap opened. The Karcher GP40 3.5 appears to be a positive displacement pump that can suck water up and that will not let water past.



Not sure, if the pump has internal overload / thermal protection it might be acceptable under the regs.

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This pump comes with a flex and a plug. Is BS7671 even relevant?

Much like they don't apply to my missus' food mixer, which has a motor bigger than 0.37kW.

And I am very grateful Sunray

Regarding overload protection, the pump is fitted with a 3A fuse in the plug - does this not help?

There is also a rather large 10uF capacitor fitted, I assume to help the motor start?

I know the pump also has a thermal cut out...

To be honest, as an alternative plan, I am wondering whether to fit a motorised valve (something similar to a zone valve in central heating), wired in with the pump. This would be normally closed, and open when the pump is switched on. Both could then operate on a timer. Would that be an easier option?

garmcqui said:

And I am very grateful Sunray

Regarding overload protection, the pump is fitted with a 3A fuse in the plug - does this not help?

There is also a rather large 10uF capacitor fitted, I assume to help the motor start?

I know the pump also has a thermal cut out...

To be honest, as an alternative plan, I am wondering whether to fit a motorised valve (something similar to a zone valve in central heating), wired in with the pump. This would be normally closed, and open when the pump is switched on. Both could then operate on a timer. Would that be an easier option?

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Once you start using it as an automatic system and connected directly to fitted devices it's no longer a portable device and the rules change.
If it was my system I would not want it running in automatic mode and ?protected? by a 3A fuse which will probably run for ever at 5 or 6A. Presumably the thermal cut-out will kick in before the fuse goes.

I don't see where you're going with the valve.

SUNRAY said:

I don't see where you're going with the valve.

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An electric valve in the feed pipe from the IBC to the pump. Normally closed, but wired in with the pump so that when the pump is switched on, the valve opened and water can flow.

This way the pump can remain plugged into an ordinary socket, no relays, no contactors, no flow switch etc. It could even operate on a plug-in timer, so it runs for 3 mins morning and evening.

garmcqui said:

An electric valve in the feed pipe from the IBC to the pump. Normally closed, but wired in with the pump so that when the pump is switched on, the valve opened and water can flow.

This way the pump can remain plugged into an ordinary socket, no relays, no contactors, no flow switch etc. It could even operate on a plug-in timer, so it runs for 3 mins morning and evening.

Click to expand...

Works for me.