FW pump pressure switch

[Keith]

I had my pressure switch for the FW pump go out last week while out
cruising. I have a Square D pressure switch, the type that's usually used on
well water pumps. Made more for 110V than 12V, the contacts arc
significantly every time the pressure comes up. Since the diaphragm pump
pulses significantly, the contactors pop 2-3 times every time the pressure
comes up. Now you can imagine over a few years how many times that happens,
especially when you're running a shower and the pump comes on every few
seconds for the duration.

Luckily for me, this particular switch has two sets of contactors, so all I
had to do was switch the wires from one set to the next. This switch was the
spare that came with the boat, so I'm guessing it has about a four year life
span. That's about how long ago I put it in, replacing the old one that had
failed.

My other accidental spare on board is a Jabsco pressure switch. I had bought
it for another purpose that didn't work out, but I'll put it in next
failure, assuming I still have the boat. Hopefully it'll work longer. I had
thought about putting a couple of capacitors across the contactors to help
with the arcing, but have no idea what to use. Anybody done this? In any
case, if you have one of these type of switches, make sure you carry a
spare.

Oh yea, symptoms are that the pump just pumps until it can't pumps no more,
then blows the breaker. It will sound like it's stopped, but it will "click"
every few seconds as it tries to keep pumping, but just physically can't do
so. You'll also see the highest water pressure you've ever seen on your
system, other than a shore water connection!

 

[Forkliftt]

Very resourceful,Half the fun of boat'n! I don't know on the capacitor- but is it possible that a 12 volt condensor from an old points system could remove the spike at start up? Just a thought.*

***Thanks for adding to Activecaptain. It is a great resource for all of us.
Steve

 

[FF]

Hit NAPA and see if an auto condenser doesn't absorb the point flash.

FF

 

[2bucks]

For those who might be inclined to try this, it is exactly what a condensor was used for in a points type ignition system. The condensor absorbs the electricity when the contacts open instead of the electricity trying to jump the gap.

The condensor case/strap is connected to the ground side and the wire end is connected to the hot lead. I know it's counter intuitive to go from hot to ground but it works for an ignition system. I've never tried it on an electric motor though. Let us know how it works out if you try it.

Ken

 

[Chris Foster]

Capacitor == condensor.* Condensor was the old radio term, and it's always been used on engine ignitions for some reason.

The question is, is the damage to the contacts happening when the contacts close or when they open.* When they first close, there's a really high current surge that may exceed what the points are rated for.* When they open, you basically have the motor acting briefly as a generator as it spins down, and the power that it generates creates an arc.

Your points are welding shut, which sounds a bit more like the overcurrent scenario when they close.* But it is possible that they're getting hot enough to melt from the disconnect arc, and then weld when they close again.

The capacitor/condensor will help IF the damage is occurring when the contacts open - it acts like a hydraulic accumulator and briefly stores the power generated by the motor, keeping an arc from being drawn as the points try to separate.

Unfortunately, if the problem is overcurrent when they close, the capacitor will make the problem worse.* Now you not only are trying to start up the motor, but you have even more current coming from the discharging capacitor.

Can you look at the points as they open and close and see if you're getting an arc when they open?* If so, try the capacitor and see if there's any difference.

You can also make use of the dual contacts on a new pressure switch if you end up with another Square D.* If the problem seems to be when the contacts close, hook them in parallel; now you have twice the current capacity.* If it seems to be when they open, hook them in series; this will shorten the duration of the arc.

You might also want to think about adding a small accumulator or expansion tank to your water system.* This will help smooth out the pulses and keep the contacts from chattering so many times.

http://www.amazon.com/Watts-PLT-5-Potable-Expansion-0067370/dp/B001AHQ9ZW/ref=sr_1_2?ie=UTF8&s=hi&qid=1225079120&sr=1-2

 

[FF]

I have found the biggest hassle is with the points opening on completion of a cycle, and the simplest solution is a large water accumulator .

With a small . or without an accumulator,, the pump is working full tilt to create the pressure and at the moment of reaching the required pressure is a very high amp load.

The load is reduced loads by a bigger tank.

For the long term cruiser the "best" is 5/8 flaired copper tubing and a quite low pump pressure setting, on at 10psi off at 20, to reduce the electrical demands with a house sized 6 gallon to 20 gal accumulator .

You may need a second pump pressure control for a washer tho.

 

[Keith]

I do have an accumulator tank, but the switch is between it and the pump. Another list suggested I move the switch, so I think I'll move it downstream of the accumulator and that will at least help if not completely get rid of the problem. I'll let you all know how it comes out.

 

[C lectric]

Too late , maybe, to offer any help here but maybe someone else.

A diode of about 6-10 amp capacity will also kill the spark upon opening. THis is large enough to withstand the backflash from the motor. The backflas is very quick and gone quickly also.* Called a Freewheeling (electrical)* or Clamping (electronic) diode in this application* Wire it so the neg side of the diode is on the positive motor lead on the motor side of the switch and the positive diode lead will go to the motor negative lead - again on the motor side of the sw.
* The motor, as FF suggested, will act like a gen., Sort of,* and can produce a nasty arc burning the contacts.*

The accumulator will also reduce the number of on/off cycles and thus the burning of the switch.* When the pressure reaches the cutoff point the shutoff will be clean
and only once untill the system pressure drops enough to restart it legitimately.* Mine is*secured to the accumulator, between the acc.* and the pump - doesn't seem to care - but piped , not hose connected right at the acc.*

These Sq D or Furnas pump control sw. , as noted , have two contact sets.* Use both rather than just the one set.* You will increase the overall life several times that of just the one set.

Do all and you will probably never see another failure* at least from this source.



-- Edited by C lectric on Sunday 24th of May 2009 06:20:36 PM

 

[Keith]

Thanks, several good ideas!

 

[C lectric]

I forgot to include that if you go for the diode get one with a PIVoltage rating of at least 400-500 volts, better if higher is available