Water pumps .... confused.

[DomDom]

Hi All

A question for the technically minded please. No onboard water tank at present, something I will fit in the near future. Anyway, looking at a kit list for this and I was going to fit an onboard pump instead of the one on the water inlet hose.
Doing some reading though and now I'm not so sure which is the best idea. Some of these newer external pumps seem to be rated with a higher flow rate than the likes of Shurflo and Whale onboard units.
The issues I want to overcome are a poor shower in the van and also get more capacity so I don't have to fetch an aquaroll in the middle of showering the kids.
The other thing I wondered was regarding the water inlet. We have the pistol grip style which seems to have a really small bore in the fitting, something which I am sure is restricting the water flow. Would I be better off fitting the older style inlet with a larger bore?
Thanks in advance
Dom

 

[Damian]

The caravan water system is designed to work at a quite low water pressure and all the pipework and fittings are rated as such.
Increasing pressure will lead to problems if too much is applied, like blown joints, damaged taps etc.
The pressure at the shower is also determined by the length of pipe to it, the number of bends, the bore of the pipe and the capacity of the shower head, along with the head lift of the pump.

It is not just a case of fitting a high flow pump and it all works,it dosent!
The maximum size pump would be a 10ltr/min at 30 psi, which is its Static pressure, not its delivery pressure.

You will never get domestic type shower pressure in a caravan unless you completely re plumb in 22mm and 15mm copper with the compression or Yorkshire fittings and replace all the taps with thse which can take the pressure

 

[DomDom]

The caravan water system is designed to work at a quite low water pressure and all the pipework and fittings are rated as such.
Increasing pressure will lead to problems if too much is applied, like blown joints, damaged taps etc.
The pressure at the shower is also determined by the length of pipe to it, the number of bends, the bore of the pipe and the capacity of the shower head, along with the head lift of the pump.

OK, these bits I understand. The main one being the bore of the pipe and the head of water which the pump can generate. The shower is the last on the line which might explain a bit.

It is not just a case of fitting a high flow pump and it all works,it dosent!
The maximum size pump would be a 10ltr/min at 30 psi, which is its Static pressure, not its delivery pressure.

I guessed there would be some kind of maximum. Mainly the pressure rating of the speedfit plumbing. How does the flow rate get affected though? As long as the pressure never goes above what the onboard pressure switch is set to, why would a pump with an increased flow rate be problematic? Incidentally, the external pump I have is rated at 14ltr/min, at least that's what it says on the side. No mention of pressure though. Strangely, when I fill the kettle from the kitchen tap (a 1 litre kettle) it takes about 12 seconds. Basic maths tells me that's about 5ltr/min.

You will never get domestic type shower pressure in a caravan unless you completely re plumb in 22mm and 15mm copper with the compression or Yorkshire fittings and replace all the taps with thse which can take the pressure

Yep, fully appreciate this. I'm not trying to get a domestic power shower experience but an improvement over what is best described as a baby dribbling (OK, it's not quite that bad LOL) would be nice. It starts off OK but once the accumulated pressure drops, so does the flow rate. I guess this means that pressure is fine as long as the flow rate will allow it to be maintained, yes?
I was looking at the pistol grip thing and the bore up the middle is only about 4 or 5mm, a far cry from the 12mm semi-rigid pipework in the van. Surely this is restricting the flow ?? Since this is the most restrictive part, and comparing the actual 5L/min with the pump rating of 14L/min....well something's not quite right.

Thanks. Dom.

 

[Damian]

Lets start with pump rates.
You say yours is rated at 14 ltrs/min, which is what it will(or should) deliver at its outlet without anything attached to it.
Now factor in the height, length and twists and turns of the pipework and you lose a lot of ltrs/min.
The size of the internal pipework is measured externally, so the internal bore is somewhat less than 12mm, probably about 6 to 8mm at best.

Pressure of the hot water is achieved by the heating, there is an air "cap" in the heater which allows the hot water to expand, which gives you the pressure.
Once you start drawing off water, the hot water is replaced by cold and the pressurised air cap is reduced, until the heater reaches full temp again, which it will not do whilst more cold water is being brought in, and remember you only have about 10 ltrs of hot water to start with.

Most problems with water pressure is due to limescale build up in the shower head, taps etc.

 

[emmitdb]

Greetings DomDom,
I'm no expert at the water systems in caravans but if I remember rightly, the smaller the aperture for the water to emerge from, the faster the water comes out (or at laeast SEEMS to come out.)
Remember what happens when you put your finger on the end of a hose pipe. The water travels further.
It would therefore apply that if you increased the bore of your shower pipe then the force would be less.