Help Me Diagnose My Water Pump Issue

[Dockhead]

I'm about six weeks into my summer cruise, and once I again I am having water pump misery I have five people on board, so water supply is mission critical

I'm posting about it because I've had a couple of dramatic fails in my diagnostic procedure this year, and I thought I would see if the collective CF wisdom can help me think this through better than I have been doing.

Here's the situation:

I field-adapted a Johnson washdown pump some years ago when my old water pump failed in an unrepairable way in a remote place when I was alone on board. I cut the spring in the pressure regulator to reduce the working pressure.

This worked fine for a few years. But then the pump started failing to switch on. Usually for a short time, then it would come on. Then worse and worse. I was able to get it to switch on if I tapped the regulator with a rubber mallet. Then it started to stick "ON" also, which would blow off the pressure relief valve on the calorifier.

I figured that the regulator was sticking where I had cut the spring.

So I replaced it last month with another Johnson pump (so that I could drop it in and not change the plumbing again), this one a proper water pressure pump with the right regulator. This one worked perfectly for a few weeks.

Then -- ! -- the new pump started doing the very same thing!!!

Like the old one, I can get it going with a rap from a plastic mallet, although this one requires a firmer rap. Unlike the old one, it doesn't stick "ON", so far.

WTF? Am I cursed? How likely is it that two pumps would fail in exactly the same way like this?

I carefully checked the electrical connections in case it was that. When the pump was refusing to run, I verified that there was power on the leads. I tightened the spade connectors to the pump. No change in condition.

So what is it? I can think of only a few things:

1. Some intermittent electrical problem. Pro this diagnosis: simple (Occam's razor), explains why two pumps were affected. Power shown by voltmeter doesn't prove that there is power with a load on. Contra this diagnosis: Why would the pump start working with a rap of the hammer? I tried pulling on and moving around the power leads, in case the hammer rap was just jogging the contacts -- nothing.

2. Some blockage in the plumbing. There is a strainer on the intake of pump. I will check it today. But would that stop the pump?

3. Bizarre coincidence of two failed regulators on two different pumps.

I can't really think of anything else.

Tips?

[Dockhead]

I've taken apart the old pump to try to understand better how the regulator works.


There is a tiny hole from the output manifold that leads to a small rubber diaphragm.


This diaphragm pushes on a metal lever which in turn pushes on the microswitch. The pressure regulation spring acts on this lever.


There is no piston and I don't see anything that could jam.


It's hard to see how it could fail "OFF". If there were blockage in the port preventing water pressure from getting to the little diaphragm, then it would fail "ON" because the lack of pressure would prevent the switch from going "OFF".


Likewise, I don't see how the theory about blockage could work. Blockage on the intake side would create vacuum which would just be more motion in the direction of "ON".



Blockage on the output side would indeed force the pump "OFF", but water flows when the pump works -- don't see how that could be doing anything. I'll try sucking on a tap next time it fails to see if that does anything.


Debris under the little diaphragm could block it in the up position, so pump "OFF". There was some oily residue under the little diaphragm of the old pump. Next thing maybe I'll pull out the new pump and see what's going on under the little diaphragm.



Big mystery.

[tkeithlu]

Hmmm.

You're looking for something that is common to the two pumps, given the (as you say) very low probability that they would both fail the same way at the same time.

There are two obvious sources of failure common to both, water in and electricity in. The water could be bringing in debris, as you suggest, or it could be bringing in air from a loose connection or empty tank. If everything it tight, the water is clean, and the tank is full, then water problems are not likely. I would expect water as a source of the problem would cause a failure always in one direction, as in always "on" or always "off."

Intermittant electricity is still a possibility, and one I'd suspect. Voltmeters require only microcurrents, while pumps take whole amps. I might straight wire the pump from a battery and see if that points to a broken wire or a corroded connection.

That's all that comes to mind at the moment.

[rslifkin]

The pressure switches on many water pumps are crap and the contacts don't hold up with the full power of the pump motor going through them. The choices are either to switch to an external pressure switch and bypass the one on the pump, or to add a good quality relay to power the pump motor (then the pressure switch only has to handle the relay coil current). Either setup should dramatically improve reliability.

[Tin Tin]

The new pump manual will likely have the wire size for the distance from your switch panel. The new pump may be more powerful than the original and wire size too small or has corroded in places, this would cause heat buildup in the contacts in the pressure switch. New wires, or use of a relay to feed off thicker wires may eliminate this as an issue. Air getting in the system from a split hose end connection, rusted jubilee clamps, tired O ring etc may also be an issue. Hoses should be double clamped. Check pump protector screen O ring.

[Dockhead]

Originally Posted by rslifkin

The pressure switches on many water pumps are crap and the contacts don't hold up with the full power of the pump motor going through them. The choices are either to switch to an external pressure switch and bypass the one on the pump, or to add a good quality relay to power the pump motor (then the pressure switch only has to handle the relay coil current). Either setup should dramatically improve reliability.

Hot tip; thanks.


Yes, perhaps a separate switch is the right approach. Would be very simple to install in my case because I have a closed off t-joint where my expansion tank used to be. Would be less trouble to source and install one of these, than to keep messing with the native one, with much better result later. Thanks.

[Dockhead]

Originally Posted by Tin Tin

The new pump manual will likely have the wire size for the distance from your switch panel. The new pump may be more powerful than the original and wire size too small or has corroded in places, this would cause heat buildup in the contacts in the pressure switch. New wires, or use of a relay to feed off thicker wires may eliminate this as an issue. Air getting in the system from a split hose end connection, rusted jubilee clamps, tired O ring etc may also be an issue. Hoses should be double clamped. Check pump protector screen O ring.

This is 24v, and the new pump is smaller than the original one. The wiring is way oversized, and is in good condition. The new pump has only a 5A fuse.

[Dockhead]

I have another possible diagnosis:


4. I don't have an expansion tank in the system -- the old one failed and the new one is complicated to plumb (different type of connectors, and spacing) and didn't get around to it yet. The new pump hardly pulsates, but at low flow rates pulsates very rapidly. Could this be burning out the microswitch contacts?


If this is the problem, then separate (heavier duty) pressure switch, and get the expansion tank back into the system, would be the solution.

[rslifkin]

The more frequent cycling will definitely wear out the pressure switch faster if the contacts are inadequate for the application.

[Dockhead]

Originally Posted by rslifkin

The more frequent cycling will definitely wear out the pressure switch faster if the contacts are inadequate for the application.

At this point, that seems to me to be the most likely diagnosis. It satisfies the condition that it explains how two pumps failed in the same way.



I've decided that I need to get the accumulator tank back into the system in any case. Today I will try to determine whether I have the fittings on board to install the other new pump, the Jabsco one, and the tank.


I'm in the middle of my summer cruise with 5 people on board, so I really want to get this nailed. If I need plumbing supplies I'll need to divert to some population center.

[Dockhead]

By now, this should be moved to the Sailor's Confessional section


This has turned into one of those mushrooming problems that turn cruises in paradise into boat repair in exotic places


So I decided that the pressure switches on both the Johnson pumps are toast, and probably because there was no accumulator tank in the system.


I had another pump on board -- a Jabsco Par Max 4. I spent a pretty long day reconfiguring the plumbing so I could get the accumulator tank in, and mount the Par Max which for some reason I thought was new.


I do so, and the Par Max runs but pumps weakly and doesn't shut off. Sigh.


Another long day ensues -- Par Max out, apart, and I rebuild it (I have the kit on board). Obviously well used -- I must have replaced the original Shure with this one years ago and just forgot. Main problem was a rusty cam bearing.


So now it works perfectly. Switches on and off correctly; pumps vigorously. Everyone showers, we do a load of laundry, and to bed.


Next morning (today) -- nothing. Pump won't run.


Out it comes again -- and rusty sludge. Obviously the motor bearing. So this one goes in the trash.


I put back the Johnson (the how many-th pump change in the last week?), hoping that with the accumulator tank in the system, the failing pressure switch will do better. It's working now. We'll see.


Meanwhile I am tempted to just kill this issue with an overkill solution like an industrial pressure switch. Like the Tival FF4. Another project (sigh) because I'll have to cut pipes and put in a t connection to plumb it in. Then I've got two lightly used pumps it would work with.


OR, maybe more rational, I just buy a new Johnson, send the current one back for warranty repair, and keep it as a spare, and do no replumbing. Probably that is the rational approach. But Jeez -- did I ever think I would spend a big chunk of my summer cruise on the WATER PUMP?? When I had complete spare pumps and lots of parts on board? Eek!

[Rjt]

The Johnson pressure switches have a very small plastic cap over the spring in the pressure switch. Picture a micro black plastic ‘top hat”. First time I tried to work on the pressure switch (loose electrical connection) I lost this. Never even knew it was gone. But the pump was erratic from then on. Replaced the pressure switch, and all good. So, just maybe, the cap went missing when you cut the spring…