Colin,
I agree, to a point. I would definitely agree in the case of a centrifugal
bilge pump. They don't develop much head and hose run and restrictions can
greatly affect output. However, Tom stated his pump is a Jabsco 36970-1000.
It's a diaphragm pump, rated at 3.4 gpm at 20 psi. I suspect the internal
check valves may be allowing some bypass, thus reducing capacity.
That's why I would try to get an idea of the output. If it's less than 80% or
so of rating, I'd look at rebuilding it or buying a new pump head assembly.
Dennis C.
>________________________________
> From: Colin Kilgour <charliekilo...@gmail.com>
>To: Dennis C. <capt...@yahoo.com>; cnc-list@cnc-list.com
>Sent: Sunday, February 24, 2013 6:59 PM
>Subject: Re: Stus-List 37+ Shower
>
>Dennis,
>
>Testing a pump against its rated capacity is pretty much a losing game
>because the ratings assume virtually no rise above the pump and they
>also assume full voltage at the pump.
>
>In most configurations, you'll have a long-ish hose run to get the
>water overboard (longer than they used in the rating process) and you
>may also have voltage drop between the battery and the pump. Also,
>when we add things like non-return valves, those also limit pump
>output.
>
>Nigel Calder does an empirical test of bilge pump capacities in his
>E&M book and the results are really eye-opening. (In sum, no bilge
>pump - in a realistic installation - delivers its rated capacity)
>
>Basically, if you want to maximize your pump output, you need to
>minimize the volume and height of water downstream of the pump.
>Problem is, most of us have already done that.
>
>Next step is to get rid of non-return valves and other things that
>restrict flow.
>
>Then voltage.
>
>After that, the pump is pretty much what it is.
>
>It'd be easier just to put a flow restrictor on the shower head...
>
>Cheers
>Colin
>
>
>On 2/24/13, Dennis C. <capt...@yahoo.com> wrote:
>> First, I would check the output of the shower sump pump vs its stated
>> capacity. Most shower sump systems pump 500 or 750 gph. Just get a 2
>> gallon bucket and time how long it takes to pump out 2 gallons.
>>
>> If it's a 500 gph pump and it only pumps 200 gph, then troubleshoot it. I
>> doubt the original build had a shower sump that had less capacity than the
>> freshwater system. Most freshwater systems pump a maximum of 3 to 3.5 gpm.
>> That's only 180-210 gph.
>>
>> Dennis C.
>> Touche' 35-1 #83
>> Mandeville, LA
>>
>
>--
>Sent from my mobile device
>
>
>
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