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Changing A Shurflo Trail King 7 Water Pump

Updated on August 4, 2016
Graham T profile image

Graham has written several books about education and is now a freelance consultant. He recently began renovating an Autoquest 270 motorhome

Changing a Shurflo pump - Introduction

When I wrote my hub 'Talbot Express Autoquest 270 Elddis Motorhome 1989' which told the story of how I renovated an older, classic motorhome,I mentioned that I was about to replace the Shurflo Trial King 7 water pump.

This was because the one that was fitted in the motorhome had a leak and it is my belief, from everything I have read, that the reason the taps are 'spitting' and the pump keeps cycling is due to air in the system.

Having drained the system down and then carefully recommissioned it to make sure there is no air, the problem still persisted and the fact there is a small leak from the underside of the pump seems to me, at least, to say that air is getting into the water system through that leak.

As I have no idea of the age of the existing pump and as they only cost £45 - £50 I decided to play safe and fit a new one, along with a new filter, rather than bother with fitting new seals and messing around with the old one.

So, here we go . . . . . this is what I did!

The old pump in-situ

Seating box housing the pump and water tank
Seating box housing the pump and water tank
The pump and water tank
The pump and water tank
A close up of the Shurflo Trial King 7 pump with its fittings
A close up of the Shurflo Trial King 7 pump with its fittings

Disconnecting the old pump

So, the first thing to be done was to disconnect the old pump.

Before I could do that, though, I had to drain down the system and make sure the freshwater tank was empty and that the Carver heating unit was also empty as it holds around 9L (2 gallons) of water.

Once I had opened the water release valve, which is adjacent to the tank, I then dealt with the water in the Carver unit and the set of pictures, below, show you the key points of doing that.

Draining down the carver water heater

This picture, above, shows what is immediately behind the flue cowl. At the bottom left corner you can see the drain plug that has to be undone
This picture, above, shows what is immediately behind the flue cowl. At the bottom left corner you can see the drain plug that has to be undone
The Carver Cascade tech plate
The Carver Cascade tech plate
You can see, in the top centre of this picture, the red temperature control wheel
You can see, in the top centre of this picture, the red temperature control wheel
The last dribble of water coming out of the Carver
The last dribble of water coming out of the Carver

Disconnecting the old Carver Cascade

Obviously, before I could fit the new pump I needed to disconnect and remove the old one and the first stage in this, which I have already mentioned, involved draining the system.

The Carver Cascade drain plug is located at the bottom left corner of the flue cowl and although it isn't necessary to actually remove the cowl, I have shown, in my photographs, what you can see if you do remove it because you can also see the temperature control). You first have to take out the four screws that hold the flue cover in place and underneath, once the cover is off, you will see what is shown in the four pictures, above.

It can take a bit of time for the carver to drain. When I drained mine it took about 15-20 minutes for the last of the water to stop trickling out.

Then, as you can see in the pictures below, it is a simple matter of disconnecting the inlet pipe (on the right in my picture) and the outlet pipe on the left.

The outlet pipe has a bulbous contraption attached to it; that is the in-line filter which I am also replacing.

The inlet connection is just a simple plastic connector that unscrews. No problem. Simple job.

The filter has a jubilee clip on the outlet pipe leading from the filter, so I had to really loosen that clip otherwise unscrewing the outlet connector was not possible as the rubber outlet hose wanted to twist as I turned the connector.

With the jubilee clip loosened, though, the filter locking nut simply turned within the pipe.

Removal

In this picture you can see the filter which is fitted to the outlet pipe
In this picture you can see the filter which is fitted to the outlet pipe
The Shurflo pump with both water connections removed
The Shurflo pump with both water connections removed

Electric Connections

Now, all that remained was for me to disconnect the 12v supply to the pump and then I was ready to remove the four securing screws which hold the pump to the floor of the vehicle.

All I had to do was make sure that the pump switch on the main control board was 'off' before disconnecting the wires.

I double checked this by turning on the taps to see if the pump motor activated.

Then I disconnected the two wires, making a note of which wire was connected to each cable in the connector block.

Then, having done that, it was time to removing the four securing screws and take the pump out of the compartment.

The empty compartment

Inspecting the old pump

As you can see in the picture above, I now have an empty compartment and it also illustrates how simple the connections for the pump are:

  1. An electrical connector block
  2. The inlet and outlet pipes.

That's it.

Although the whole pump system looks tricky, it is, in fact, one of the simplest parts of the motorhome and having reached this stage, I knew that the reverse operation (fitting the new pump) would be a doddle.

First, though, let's have a closer look at the old pump in the pictures below

Signs of water leaking

The underside of the pump with signs of water damage
The underside of the pump with signs of water damage
One side of the pump, also showing signs of leaking
One side of the pump, also showing signs of leaking
The pressure adjuster screw
The pressure adjuster screw

Leaks

You can see in the first two pictures very definite signs of water that has leaked from the seal at the bottom of the pump. This backs up my suspicion which first came about as there was a regular pool of water in the compartment where the pump is housed.

It was only ever a small pool; no more than a few teaspoons of water, but enough, nevertheless, to de-pressurize the system and allow air in.

The third picture is an interesting one, though . . . . .

Old Vs New

The pressure control screw on the new pump
The pressure control screw on the new pump
The pressure control screw on the old pump. Notice the essential difference?
The pressure control screw on the old pump. Notice the essential difference?

Pressure Switch

When you look at the two photos, above, they show the same section of both the old and new pumps.

The unit on the end of the pump, where that central screw goes in, is the pressure switch.

Inside the unit is a small diaphragm which, when water presses against it, pushes against a very sensitive switch and that, in turn operates the pump and sends water pumping to whichever tap(s) is being operated.

And the purpose of the central screw is to adjust the sensitivity of the diaphragm/switch when water presses against it.

It does nothing to alter the actual flow rate of the pressure in the system; it's main job is to control how sensitive the diaphragm is to pressure flowing against it.

And the interesting thing in those two pictures is that on the new pump, the screw is fully in, meaning that the diaphragm is at its most sensitive setting.

In the picture from the old pump, though, the screw is fully out.

And that tells me the most likely reason is that a previous owner was experiencing 'cycling' (when the pump randomly switches on for a few seconds every few minutes) and so they followed the much written about solution of making the diaphragm less sensitive, by reducing the switch pressure (turning the screw anti clockwise).

In some cases that is a good solution but, unfortunately in this case, they looked no further and failed to investigate the possibility of air trapped in the system, either through a poor water connection, or through a leak, and so they never actually solved the problem.

In all probability they reduced the problem a little and I would imagine that after they had turned the crew to its 'out' position, the cycling was less frequent, but it was still there.

As was the real culprit - the leak.

The New Pump

Thew new shiny pump
Thew new shiny pump

The New Shurflo Trial King 7 Water Pump

In the picture above you can see the new Shurflo pump just waiting to be fitted. In the box was not just the pump but two new inlet connectors also. At the top you can see the outlet pipe connector (on the left when the pump is flat) and at the bottom you can see the inlet pipe connector.

And in the picture below, you can see the two connectors that come with the pump.

These are to allow you to connect the inlet or outlet pipes either from or to a straight pipe coming to or from the pump or, as you can see in the picture at the top of this hub (where my old pump is connected) if one of the pipes is coming in at a right angle to the pump or leading away from the pump at a right angle, these connectors allow you to deal with that.

The connectors

Connecting the new pump and filter

So, all I have to do now is the reverse of disconnecting the pump.

Firstly I connected the inlet pipe, which was an easy enough task and then it was time to fit the new filter.

Water inlet ready to be fitted

Ready to fit the filter and the outlet connection

The filter and outlet connection

So, the water inlet pipe has been connected and sealed with plumbing tape and the outlet side is now ready for the new filter to be fitted and then I can make the final tube connection.

In in the pictures below you can see the difference in design between the old filter and the new one.

One thing I had to do was trim the pipe by about two inches (5cm) due to the fact the the new style connection on the new pump made the whole connection longer and so to avoid kinking the outle tube backwards and straining it, it was necessary to alter it slightly


The final connections

The new filter
The new filter
New and old side by side
New and old side by side
Outlet pipe trimmed, straight connector fitted and ready to connect
Outlet pipe trimmed, straight connector fitted and ready to connect
Straight connector fitted to the new filter
Straight connector fitted to the new filter
At last . . All connected. Job done!
At last . . All connected. Job done!

Commissioning

So, now the new pump and filter are all connected and it should all be ready to go. The whole job really was simple and took no more than an hour.

It would probably have been 30 minutes if I wasn't talking photos every step of the way!

And now for the real test.

When I filled the tank back up would everything work properly without leaks? Only one way to find out.

As the system is empty, the whole thing has nothing but air in it so, as well as filling up with water I have to make sure all the air is out of the system.

I opened the two hot and cold taps and then filled the tank.

Four minutes later and the tank was full.

Now to remove the final bit of air between the tank and the taps and fill the Carver Cascade water heater tank.

i closed all the taps except the hot tap in the kitchen, then I switched the pump on and with the kitchen hot tap open, the pump whirred into action.

For a few seconds, the water that was still in the system between the pump and the taps came out as a slow, steady flow and then, once that had cleared, the air came through - a few seconds of spitting water and then, a nice, smooth steady flow. No spitting, no pressure or flow rate fluctuations, just running water!

Yes!

Next I repeated the process with the hot tap in the shower room. Same result.

The cold water taps followed and no more than five minutes after connecting the new pump, I had water that was flowing properly from all four taps; no spitting, no variable flow rate. Just a steady, consistent flow of water.

Once the hot taps were opened, the Carver filled and then I switched the gas supply to it back on and quite soon, just 10 - 15 minutes and the water was already warm.

A final inspection of everything showed no leaks and so it was then just a matter of putting the cushions back on the dining area seats, tidying up, tools away and then a well deserved cup of tea!




© 2016 Graham

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