In recent years Swift has largely moved away from external submersible water pumps in favour of on board pumps. The new pumps work in a different way from the old. Instead of spinning a submerged impellor at high speed and giving the smooth flow of water the new pumps contain 3 or 4 pumping chambers that pump in sequence each delivering a small volume of water to the outlet. This gives a continuous, but somewhat pulsing, flow of water.

This type of pump is known as a positive displacement pump as the fluid is positively displaced out of the pumping chambers and one-way valves prevent it going back again. The effect is to produce a good delivery pressure. The pumping action is achieved by flexing a rubber diaphragm which forms a part of each chamber. For this reason the pumps are often referred to as diaphragm pumps.

As well as delivering a good pressure this type of pump has other advantages. Firstly, the delivery pressure is not adversely affected by small changes in the supply voltage so performance should be roughly the same whether on a mains hook up or in a field with battery.

Secondly, positive displacement pumps can suck water from a source several feet below them. This means the pump can be mounted inside the caravan or motorhome away from the worst of any frost and possible contamination. All that is needed in the Aquaroll is a suction pipe with some form of filter on the end.

Lastly, diaphragm pumps can normally run dry without any problems.

If there is a downside to diaphragm pumps it is that they can be noisy. Someone one said his sounded like a machine gun on steroids. They don’t have to be that noisy; much depends on how they are installed and used.

All diaphragm pumps ‘knock’ when operating so it’s important to try and dampen this through soft mountings such that the noise does not get transmitted to the bodywork. I think its fair to say that Swift has not always given this aspect of installation as much attention as it could have.

The pumps should ideally be mounted onto a board via rubber feet or grommets so that the worst of the vibration is not carried through to the board. The board itself can also be mounted in the same way to reduce noise transmission further. Also pipework near to the pump should be kept from touching anything that might amplify the noise. 

All these things will help to reduce the amount of noise heard but the other factor in determining the noise level is how hard the pump is working and, in particular, whether it is sucking in any air.

Flojet pump
Flo-Jet pump installation in a Swift Challenger

One problem with the Truma systems Swift supply is that the little blue suction filter on the end of the Aquaroll hose tends to float to the surface allowing air to be sucked in. Various ideas have put forward to get round this but the simplest is probably to get a suitable length of 22mm plastic conduit from a hardware store and thread the pipe through it. An alternative would be to swap the plastic filter for a charcoal one such as those made by Whale. These are much heavier and have the added advantage of helping to take any unpleasant tastes out of the water. Beware though that the slight extra restriction caused by a charcoal filter could make the pump a fraction noisier.

The other problem with the Truma inlet pipework is that the plastic pipe can partially pull off (unseen) from the spigot inside the connector itself. Should this happen then air can be sucked in at this point.

As already mentioned the noise a pump makes can be related to how hard the pump is working. If there are restrictions in the pipework these can put extra load on the pump. It's also helpful to try and reduce the number of right angle couplings as they too cause a certain amount of drag on the water.

Pump vibration can also often be reduced by fitting a device known as a surge damper to the pump outlet.

The detail of these varies but the net effect is to absorb and smooth out the pulses of water created by the pump. This results in a smoother delivery of water to the taps, less noise and a more reliable operation of the pressure switch (see below).

The Shurflo diaphragm pumps installed by Swift for a short time in 2008 were all fitted with surge dampers. These took the form of a horizontal black cylinder with a tyre valve on one end – see pic.

The Flojet pumps installed since then are not fitted with surge dampers as original equipment it is said that the internal valve arrangement makes them unnecessary. However my experience is that, even here, fitting a surge damper can do much to help improve performance in the way described above.  

There are two common types of surge damper – the Shurflo/Fiamma design and the Whale type one.

Shurflo damper
Shurflo damper
Whale damper

The first works by having a flexible rubber diaphragm behind which air is trapped under pressure. This pressure can be adjusted with the help of a tyre pump. In use the water acts against the other side this diaphragm, which then absorbs the pulsing and helps to even out the water pressure. The air pressure behind the diaphragm is normally set to about two thirds of the pressure at which the pump cuts out. In cases where the Shurflo pump and damper were a factory fit the pump pressure was set to 30 psi and the diaphragm to 20 psi. This type of damper, sometimes known as an accumulator, is very effective.

The Whale type damper has to be mounted vertically and works a bit like an upside down pop bottle. Water pressure at the bottom compresses the air inside the damper housing doing away with the need for a diaphragm and air valve. It has a much smaller capacity than the Shurflo one but nevertheless works quite well. One point to be aware of is that, in prolonged use, the trapped air can get absorbed into the water thereby reducing the efficiency of the damper. Periodic draining of the water system can help to avoid this.
Whale Damper

A noisy pump is one thing, an intermittent one something else altogether. We’ve all been there. You switch on the tap and nothing happens or, worse still, you’re in the shower at this point. Then a few seconds later the pump suddenly starts and scalding water comes out of the shower head. Alternatively you switch the tap off and the pump keeps on running for ages before switching off. These symptoms all point to the pump’s pressure switch not being adjusted properly.

It’s the pressure switch that switches the pump on and off and it does so according to the water pressure in the pipework to the taps. When the water pressure reaches a certain level the pump is automatically switched off. The water cannot escape back through the pump so, if the taps are shut, the water stays trapped under pressure until a tap is turned on again. When this happens the water pressure falls and the pressure switch puts the pump on again to maintain a flow of water to the tap.

This is a simple arrangement and has the advantage that micro-switches to switch the pump do not have to be incorporated into the taps thereby improving reliability and giving a wider choice of taps. However it does depend on the pressure switch operating at the right time. SOC members’ experience is that this does not always happen.  The good news is that, in the case of the systems fitted by Swift, the pressure switches can be adjusted.  They actually form an integral part of the pump and can be adjusted with the help of a suitable screwdriver.

Photo courtesy Swift

So, if your water pump seems temperamental, it may be worth adjusting its pressure switch. Before doing that though make sure that the system is properly primed and that any air has been expelled.

On the Shurflo pump the pressure switch adjusted by rotating the centre screw on the end housing (see below). Turning the screw clockwise increases the pressure at which the pressure switch cuts power to the pump, turning anti-clockwise will reduce it. Do not turn clock wise beyond the point at which resistance is felt as this could result in damage to the pump or water system.

Shurflo adjustment
Shurflo pump adjustment
Photo courtesy Swift

On the Flojet pump adjusting screw is hidden behind a plastic cap. This needs to be removed by unscrewing its retaining screw. The pumps are usually mounted vertically just off the floor so it may be necessary to release the mounting screws to access the cap.

Turning the screw clockwise will increase the pressure at which the pump switches off; turning the screw anti-clockwise will reduce it. A maximum of 1/4 turn either way is recommended

For Swift Group caravans built before October 2008 additional rubber feet for the pump are available under part number 1086640.

Flojet adjustment

Flo-Jet pump adjustment

If a Truma Flo-Jet pump is fitted and it pulses Swift recommend fitting a surge damper. The parts needed for this can be ordered via a Swift dealer as follows:
1088201 - Surge Damper;    1088202 – Bracket;    1010411 - T Piece adaptor.