Water Pump Running Every 30 Secs

[Helipilot100]

Just got a new to me 45 ft motor cruiser. There are two switches for the water pumps and when the system is pressurised they come on about every 45 secs. If I switch either of the two switched off it still happens but obviously when both off, it stops. I’m assuming a leak somewhere so my questions are, is there an easy way to trace where as everything is so tightly packed in the bilges. Could it be something else? Any help would be much appreciated. Thanks in anticipation. The boat is a Searay 420 ac.

 

[Minerva]

That sounds like you have a leak and the pump is running to maintain pressure.

I think you'll have to start at the Tank/pump and work your way forward checking every water pipe individually to their respective taps to trace the leak.

 

[Skipper_Christoph]

If you have a leak in the pressurised system the water has to go somewhere. Are your bilges filling up with water?

 

[Boathook]

Sometimes the pumps themselves may be the cause by allowing the pressurised side back to the low pressure side, normally through the diaphragm; if the bilges are dry.

 

[pandos]

Sometimes debris can affect the pressure switch on the pump itself..just taking it off and cleaning it will usually fix this, but if the water flows from the taps when wanted, then let the pumps run as they are until water is found in the bilge....as others have said if it is escaping into the boat it will probably end up in the bilge eventually.

Have you looked around for an obscure connection to an anchor wash or an outside shower or something that could be leaking overboard.?

 

[RupertW]

On a sailing boat the culprit almost every time is the swim shower fitting on the stern which usually has it’s own stopcock which solved the problem.

 

[jaminb]

Is your auto bilge pump running with similar frequency? Check the hotwater pressure relief valve overflow.

 

[Graham376]

May be the prv (pressure relief valve) on the calorifier as it's not restricted to one pump.

 

[Bilgediver]

If the pump is running as much as that then maybe as well as a small leak you need to replace the lost air in the accumulator especially of no leaks found. When the accumulator has sufficient air the pump does not cycle so much. The accumulator will be a cylindrical vessel sitting on the delivery line from the pump. Should have a connection on top to pressurise.

 

[RupertW]

If the pump is running as much as that then maybe as well as a small leak you need to replace the lost air in the accumulator especially of no leaks found. When the accumulator has sufficient air the pump does not cycle so much. The accumulator will be a cylindrical vessel sitting on the delivery line from the pump. Should have a connection on top to pressurise.

And may be worth bypassing the accumulator to see if it still happens (once you have checked small leaks everywhere else starting with outside shower/anchor wash.)

I had to bypass the accumulator 7 years ago when it sprung a leak. We got a new accumulator fitted and it took us a while to realise they had fitted it still bypassed. So it’s sat as an ornament every since as there seems to be enough pipe work throughout the boat to allow a decent amount of water to come out before the pump kicks in again.

 

[Slowboat35]

Suggestion for leak check - I'm sure you've looked for stray water in the bilges, switched bilge pumps off etc. Put dry newspaper 'downhill' of thewater system in the bilge to dentify any stray water.

You can estimate the amount of water that might be leaking (to give you an idea of how much - or rather little you need to be looking for) by switchng pumps on until pressurised and drawing water from a tap into a container until the pumps restart. It should allow a glassfull or so, if its only a few spoonsful it suggests an accumulator pressure failure. That procedure indicates he amount of water loss that triggers the pumps. It won't be much, you're not looking for a deluge by any means, a hard to spot trickle may be enough.

If you're happy there isn't a leak it is more than likely that one or both the pumps are allowing pressure to backflow through themselves due to wear or poor sealing of the internal non-return valve . This is easily proved. Pumps on. Give a convenient tap a quick open/shut and note rate of flow. Pumps off. Immediately repeat the tap exercise.The flow should be the same. (if not- report back here!) Repressurise. Wait for a minute. Try the tap again - any difference? If unsure repressurise and wait 5 mins before trying the tap exercise again. Any loss of pressure will be obvious.
If you don't have an external leak then you must have a internal one - most pumps can be revived with a service kit.
I do emphasise that (especially if the accumulatore pressure is low too) the amount of water-loss to trigger the pump can be very little indeed.

Repressurising an accumulator is sometimes easier said than done as they tend to get stuffed into corners. It'll have a standard automotive schraeder valve to fit a footpump and you'll need an accurate tyre pressure gauge plus have to know the correct pressure to set it to. Frankly if it looks old and grotty I'd just replace it. They don't last forever.
To set it up you'll need to know the pump's cut-in pressure setting (the low pressure at which it starts running) and set the accumulator pressure at about 3psi below that. It's easy enough to determine the cut-in pressure if you can identify the pump and look up it's spec on t'internet but most seem to cut in at 20psi so a pretty standard accumulator setting is 17psi. They usually come ready-pressurised.

There is nothing more irritating than an unreliable water system . In my experience if the pump/s and accumulator look old and rusty you'll save yourself a great deal of time, effort and worry in the future by simply replacing them. Like for like replacements are usually possible and minimise the scale of the job. It's readily diy-able.

 

[johnalison]

On a sailing boat the culprit almost every time is the swim shower fitting on the stern which usually has it’s own stopcock which solved the problem.

I don't have a stern shower fitting. There are plenty of other potential sources of leaks though, but as of the last five years I have been free of them. One odd one was when the pipes meeting the hot manifold became brittle over time and needed replacing. I doubt if the accumulator is relevant, unless it itself is leaking, which has happened to me in the past.

 

[Bilgediver]

There is also a possibility that one of the pumps has leaky valves and the water is flowing back through the pump to the tank. It has happened before.

However definitely check and repressure or replace the accumulator as it is there to stop cycling caused by minor leaks.
The new accumulator may need to be charged to the right pressure for your system as described above in order to do its job properly.

 

[Amlov]

When we first got our boat, the water pump did exactly as you describe. As I didn’t have a leak, and to be honest if yours is running every 30s I doubt that you do as this would be a large/obvious leak, I took the pump apart. On the pressure diaphragm there was an adjustment screw to allow you to set the pressure at which the microswitch operated. I adjusted this so that it cut out at a lower pressure, I assume it was pressurising to a high value and slight leakage back through the valves was forcing it to restart so rapidly. Now it only runs every 8h or so - typically about 5am.

 

[Helipilot100]

Thanks to all for the advice. I'm heading back out to the boat Sunday (its in Croatia and I'm in Scotland!) Ill check all the things mentioned. I suspect a leak as the bilge pumps did seem to be coming on a regular basis. All the replies are much appreciated. Thanks!!!