Placement of electric pump in fresh water system

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jwdorst

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Does anyone have any advice to offer regarding the placement of an electric pump (Jabsco Sensor Max 14) in a fresh water system. In other words does it make a difference, performance wise, whether the pump is installed close to the tank (ie creating a short suction length and long discharge length situation) or close to the tap (creating a long suction lenght and short discharge length situation)?

Thanks.
 
if you put the pump close to the tank you can use a shorter piece of non-collapsable hose, which is cheaper than the re-inforced hose for the discharge side. Performance-wise it shouldn't make a difference cuz you're not moving that much water so friction loss is not a concern; is the pump above or below the tank?
 
I agree with Tara_Vana re the collapsible hose but the other issues are noise and length of wiring run. Don't forget ease of servicing, as well. No pumps are 'fit and forget' though the Parmax 3 and 4 pumps that we are using come close to it.
 
Disregarding cost of hose for a moment (although a valid point), I would prefer to locate the pump about 5 meters (15 feet) from the tank, and approx. 1.5 meters (4.5 feet) above the bottom of the tank. The pump would then have to discharge through 1-6 meters (3-18 feet) to various taps.
 
Welcome to the forum. It would be helpful if you could say a little bit about yourself in your profile?

As to your post - Why?
 
I would like to mount the pump in the same area as I have mounted my calorifier, batteries and refrigeration compressor. Keep everything together, simplify wiring runs etc. Just wondering if any impact on pump performance is to expected (i.e. are displacement pumps generally just as efficient on the suction side as they are on the discharge side?).
 
I would tend to put the pump near the tank. 1.5 Metres above the tank may give you problems with priming and poor pressure (pumps are better pushing than pulling !).
 
Would totaly endorse that.

Have just done all this type of installation & the jabsco engineers agree.
Put the pump as close to the tank as poss & with a flooded suction.

oh by the by I also put a Shureflow filter system in as well, but took a connection of to the Loo basin/shower before the filter to avoid the pressure loss.

good luck

poter
 
As long as you have a flooded suction it does not really matter. What is more important is that the capacity/performace of the pump matches your system.

Ensure that your pump and accumulator match your outlets. Otherwise you may one day just put a drop of water in your whisky whist the wife is in the shower and ---- misery.
 
Water is incompressible so provided the hose doesn't collapse the main potential problem with your proposal is priming. Does the pump data sheet say what the maximum self-priming head is? Stay well within that to allow for valve or vane deterioration over the years but otherwise I don't see any problem.

I have two water tanks, the smaller one of which is six metres from the pump and the bottom of that is around 1m to 2m below the pump and I have no problems. We always let that tank suck air and it always re-primes (though there is a higher head when the tank is full).

I am using the Parmax 3 - check to see whether yours will prime with a reasonable head.
 
[ QUOTE ]
I would like to mount the pump in the same area as I have mounted my calorifier, batteries and refrigeration compressor. Keep everything together, simplify wiring runs etc. Just wondering if any impact on pump performance is to expected (i.e. are displacement pumps generally just as efficient on the suction side as they are on the discharge side?).

[/ QUOTE ]

Unless its a true positive displacement pump ... I would suggest not putting it above tank bottom level and would also suggest you site as close to tank as possible.
Very few pumps like to drag product to them and especially UP HILL ... Do it and yourself a favour ... site it at base and close to tank.
 
Although my first thought was also that pumps are generally better at pushing than pulling (and this was the reason for my post), this doesn't really make sense considering that, by definition, the same amount of water has to be pulled and pushed. I suppose then that head pressure has nothing to do with where the pump is placed in the system, but is simply a function of vertical lift that needs to be overcome by the pump and resistance in the system.

Priming then appears to be a separate issue to consider and, once resolved by using the correct pump type and capacitiy, should be left out of the equation.

The technical information for my Jabsco Sensor-Max 14 specifies self-priming up to 10 feet suction lift.

Based on the input received from all of you, I think I'm going to go ahead as planned.

Thanks!
 
"Does anyone have any advice to offer regarding the placement of an electric pump (Jabsco Sensor Max 14) in a fresh water system. In other words does it make a difference, performance wise, whether the pump is installed close to the tank (ie creating a short suction length and long discharge length situation) or close to the tap (creating a long suction lenght and short discharge length situation)?"

You have answered your own question in a way.

A 'pump' is not a suction device (either in a boat or elsewhere), other than when used as a puddle pump. They are most efficient when 'pumping', so best placed as close to source to be discharged as possible. Pump data/graphs, usually combine lift head/discharge pressure, not suction.

One problem to be considered, is the number of possible leakage points upstream on the pressure side of the pump (including the shower on the transom sugar scoop), either from poor connections or taps left on un-noticed when the pump has been switched off. Has been known to drain the tank &/or fill the bilges. Best not to leave the pump on continuously when offshore.

If you placed your pump at the tap (highest point), any leakage would anyway result in that bit draining down, losing prime & then pumping air.
 
If the hose line is primed then I can't see that the location of the pump in the line makes any significant difference.

However if you want (as you do) to mount it above the tank, then there is the issue of priming. Assuming the pump will self-prime then clearly the closer to the tank it is the better. Once it's primed then you should be fine.

If you really want to fit it above the tank and find hand priming/repriming necessary, then you can always fit a check valve. I'm not generally keen on these as they restrict flow a bit and can go wrong, but it would solve the problem if priming is an issue. However, as previous posters have advised, it will all be a lot easier, and your pump will last longer, if you put it below the tank.
 
[ QUOTE ]
However, as previous posters have advised, it will all be a lot easier, and your pump will last longer, if you put it below the tank.

[/ QUOTE ]Why do you think that the pump will last longer?
 
Absolutely no problem with siting the pump above the tank, provided it is designed as such, my boat was built like this, although the height above tank bottom on mine is only about a metre. The original pump was replaced last year, after 20 years of service.

There is more of a problem with siting it some distance away. The suction pipework resistance will tend to reduce the head available at the pump. This may give a lower discharge pressure, although this is less of a problem with a positive displacement pump than it would be with a centrifugal one. However, it will almost certainly reduce the flow rate given by the pump. If you are committed to this position, make the suction pipework as large and with as few bends as possible to minimise resistance.
 
[ QUOTE ]
There is more of a problem with siting it some distance away. The suction pipework resistance will tend to reduce the head available at the pump. This may give a lower discharge pressure, although this is less of a problem with a positive displacement pump than it would be with a centrifugal one. However, it will almost certainly reduce the flow rate given by the pump.

[/ QUOTE ]Can you explain why it makes any difference whether the pipework resistance is mostly on the inlet side or the outlet side of the pipe (always assuming that the pipe does not collapse and no air gets in)? If the pipe were of a hard material, say copper, I can't see that it would make one jot of difference.
 
Because a reciprocating pump's performance is particularly sensitive to Net Positive Suction Head (NPSH). Locating the pump above the tank and at some distance from it may bring the NPSH required of the pump below the NPSH available from the system. Cavitation will then occur in the suction of the pump, plus increased losses in the valves. Although head will not be affected very much, flow will.

As a rule of thumb in industrial applications, you should always calculate the available NPSH if:

the pump is installed above the liquid level
the pump draws from a tank under vacuum
the liquid has a high vapour pressure
the suction line is unusually long
the plant is at high altitude (reduced atmospheric pressure)

Pumps for boat domestic systems are not designed to very high standards, so NPSH requirements are quite high. A kink in a suction line will almost certainly cause cavitation in the pump.
 
I see where you're coming from now...but those effects are almost an order of magnitude away from anything you see in a yacht. As for kinks or whatever in the suction pipe, yes, that is accepeted and he is going to use suitable pipe.
 
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