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Old 08-27-2016, 12:14 PM   #1
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Freshwater pump losing pressure

Kind of stumped on this one. Our freshwater Jabsco 36800 pump just started loosing pressure. It does not pump at the pressure it normally does and consequently less water volume which then reduces water flow to our Masterflush heads and any faucet on the boat. The pump runs but at much lower pressure. I cannot seem to figure this one out. No kinks that I can see. Could it be electrical? If so, where to start checking. Batteries are all reading as fully charged.

Any thoughts?
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Old 08-27-2016, 12:17 PM   #2
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first look at any screen filter on the input side.
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Old 08-27-2016, 12:36 PM   #3
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Will check all screens and lines again. Thanks.
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Old 08-27-2016, 11:47 PM   #4
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HOw does it sound? Compared to before you noticed this, is there a change in the sound such as running slower. You may not have noticed of course untill you realized there is a problem.

Wiring could affect the pumps operation if there is too much Vdrop in the electrical. Try measuring the voltage at the pump .

From the batteries there will be some drop but should not be much, no more than 1/2 volt. If there is much more then maybe there is a loose or a dirty connection.
Both the negative and the positive leads need to be checked.

Maybe what is happening is due to excessive Vdrop the motor cannot get enough power to operate at normal rpm. When you turn on the tap the pump cannot run fast enough to supply the water volume which will be perceived as low pressure and a low delivery rate.
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Old 08-28-2016, 01:01 AM   #5
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As bayview said, check that nothing is keeping water from getting to the pump.
If you don't have a blockage, there are a bunch of other things that go wrong with those old belt driven pumps.

The valves always go bad eventually.

The little belt pulley sometimes gets loose on the motor shaft. The pulley slips and the belt doesn't move as fast as it should.

The diaphram stretches out.

There is a bearing at the top of the rod. If it wears out the eccentric won't move the diaphram enough.

The pulsation dampeners in the bottom of the pump collapse and make the pump act funny.

If the intake line is clear, take the pump apart. I bet you'll find the problem. It is a simple pump and kind of fun to work on.

Be very careful putting the pump back together. It is very easy to crack the plastic housing if you over tighten the screws.
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Old 08-28-2016, 09:11 AM   #6
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Rubber diaphragm does the work. Flapper valves (same principle as dinghy pump) allow water in and out. The problem is likely one of these.
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Old 08-28-2016, 10:35 AM   #7
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C lectric, the pump does not run at the same rpms or sound the same, so I am tracing all wiring and checking connections.

The pump is a new install from last year so I am not sure about any diaphragm issues but will keep that on the list for the next thing to check.

I cannot get back. My boat until this coming Thursday so I will keep all of this on hand as I compromise to work on this.

Thanks for the ideas and help!
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Old 08-28-2016, 10:53 AM   #8
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check the pipe from tank could be muck in the tank, it must flow freely, if so its pump. spend some money for a new one. Job done
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Old 08-29-2016, 12:09 AM   #9
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Kolive,
I thought of the Vdrop because I had that situation several months ago. There was no obvious corrosion seen but after undoing and cleaning connections, voila, the pump ran nicely again.

If that is not the problem then the other suggestions should be looked into.
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Old 08-29-2016, 12:42 AM   #10
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C lectric, that was my first thought but electricity is my least area of system knowledge that I learn a lot about every time I face it.
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Old 08-29-2016, 08:39 AM   #11
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" that was my first thought but electricity is my least area of system"

Go to Radio Shack or a box store and purchase a VOM.About $10 and read its book.
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Old 08-29-2016, 03:03 PM   #12
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FF,

Thanks, I have a VOM and use it regularly. I just don't think my confidence in all things electrical is as strong as I would like. I also have Nigel's book and 12 volt bible which I read and refer to.
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Old 12-30-2016, 11:37 PM   #13
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Did you ever find out your problem...I have the Same thing except on Two pumps...Whale UF 1215, 3.3 gpm....they are down to .8 gpm....no debris in screen, water flow from tank is fine....both pumps are less 2 years old. Do the diaphragms get weak...we use the boat about once every 2-3 weeks for weekends mostly. Batteries are 3 honking AGM house batteries...relays near pump aren't warm.....puzzled.
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Old 12-30-2016, 11:58 PM   #14
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Remove the pump, run it outside your circuit using a battery and a water bucket so you will know if the issue is the pump itself or anything elsewhere on the water circuit. At least you will know where is the issue, will only remain to find the issue...
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