Next caravan DIY project - external drain valve

Aug 24, 2020
290
163
4,735
Visit site
Hi all, looking again to tap into the collected wisdom of the group...

Since Gozza Junior has reached the age when he can decide not to come caravanning with us, we've turned our front lounge into a fixed bed, by removing the cushions and installing a permanent mattress, which is better for Mrs Gozza's back, and saves moving stuff around morning and evening.

One consequence of this, of course, is that operating the water system drain-down valve is a major pain. The valve I have,as far as I can tell, is this one:
drain valve 2.jpg

I'm considering replacing the clear pipe (which comes through the caravan floor) with a longer section of proper caravan water pipe, leading to a tap which is easily accessible outside the caravan - probably the sort used on motor homes to drain the internal waste tank. Then when it's time to go home I can open the valve and drain the tank without doing contortions to get to a valve which is now hidden.

My thoughts so far are:
1) I considered replacing the valve with a three-way T fitting, but decided I wanted to keep the option of being able to close the valve inside the caravan, for example if the external pipe became damaged.

2) I know I need to think of a way to keep external parts clean and protected from road dirt.

And my questions...

1) Am I laying myself open to huge problems in the future of any kind? I can't see any way this could lead to water contamination as long as I flush out the "dead leg" every time I set up the caravan

2) Is there an easier way of achieving the same thing?

3) Has anyone done this and what advice would they have?

I know some people will be thinking, why not just travel with the water tank full, it's only 10 kg? Not an option for me, I already have enough trouble achieving nose weight as a previous owner of the caravan removed a bunk bed from the back end to make the 'van from a five berth to a four berth, and I've replaced a sliding wooden partition at the back end with a curtain!

(EDITED twice for clarity and spelling!)
 

Damian

Moderator
Mar 14, 2005
7,510
936
30,935
Visit site
The idea is sound.
The only problem I can see is what kind of pipework would work as the drain pipe as fitted is not very big diameter wise and any other drain tap is likely to be a bigger diameter, but with some thought and various reducers is achievable.
This tap would be ideal as it has a dust cap which would keep road dirt etc out of the pipe, but reducing from 28mm to the Truma tap would involve some making of a step down reducer:


Quote " know some people will be thinking, why not just travel with the water tank full, it's only 10 kg? "
Yes some people will say that , and if the tank was baffled then it may make sense, but the tank is not baffled and having 10 ltrs of water sloshing about as you drive is very likely to cause damage such as ripping the screws out securing the tank , or worse which is why it is always advised to empty the tank for travel
 
Mar 14, 2005
17,848
3,221
50,935
Visit site
Hello Gozza,

Your suggestion fails to recognise the safety job of the valve you have pictured. It has two functions, firstly as a drain valve as you have suggested, but its second function is a 3.5Bar pressure relief valve which dumps if the pressure in the system rises too far, either by an over excited pump, or if an appliance starts to boil water and generates excess pressure.

With your suggested scheme, if excess pressure were to build up the exit route would be blocked by your down stream valve.

You need to find a way to relocate the valve so you can access it.
 
  • Like
Reactions: Gozza2
Jun 16, 2020
4,819
1,940
6,935
Visit site
Agree with the Damian. I tried a different version of this some time ago. Being far less flexible than I used to be I hate having to lie on the floor to reach the valve, also not keen on reaching under the van. So I ordered a 12 volt solenoid valve with the hope of being able to drain at the flick of a switch. Problem was, the valve is designed to work under pressure so not free flowing. I would still like to do that mod if anyone knows of a better valve.

But I may do as you suggest, but Use a bend to bring the waste Near th the side of the van and within reach.

John
 
Aug 24, 2020
290
163
4,735
Visit site
... So I ordered a 12 volt solenoid valve with the hope of being able to drain at the flick of a switch... I would still like to do that mod if anyone knows of a better valve.
Thanks John - looks like this could be a solution to the problem, if I could one that would allow flow and was fitted in addition to the existing valve - so the existing valve covered the safety task (and was available for backup if the solenoid failed), with the solenoid valve allowing draining under normal circumstances. Some googling needed me thinks...
 
Jun 16, 2020
4,819
1,940
6,935
Visit site
Gonza2, I am a bit concerned after the profs post. I did not know that the dump valve is also a pressure relief valve. I tried to research this and think I have found that Truma heating have a separate Pressure release valve, but Alde use the dump valve. I can understand the concern Re heating butt can’t see a caravan pump achieving high pressures if they got left running.

Certainly something to take into consideration.
 
Jun 16, 2020
4,819
1,940
6,935
Visit site
Thanks John - looks like this could be a solution to the problem, if I could one that would allow flow and was fitted in addition to the existing valve - so the existing valve covered the safety task (and was available for backup if the solenoid failed), with the solenoid valve allowing draining under normal circumstances. Some googling needed me thinks...

But if you added a solenoid valve as you say, then the existing dump valve would need to be left open. Then it would not work as a pressure relief valve.

Another idea, for those technically able, is to rig up a linear actuation motor to operate the existing valve lever. That’s food for thought.

John
 
Aug 24, 2020
290
163
4,735
Visit site
But if you added a solenoid valve as you say, then the existing dump valve would need to be left open. Then it would not work as a pressure relief valve.
Sorry, didn't make clear what I meant! What I was thinking was to leave the existing valve untouched - Tee off from the pipe between the caravan water inlet and that existing valve, and take the solenoid from that Tee.

Having looked at a few solenoid valves (all of which needed approx 3 psi to ensure flow), I've modified my thoughts to tee-ing off as above, and piping from the tee to a valve in an accessible location. So the system can be drained by EITHER opening the existing valve (or it opening by itself under excess pressure), OR by opening the new valve that I've just put in on a spur. Or both, I suppose, but that seems a bit pointless!

I still like the idea of a solenoid if a usable one can be sourced, but only because I'm a gadget freak and it gives me an excuse for another switch on "the panel" (I even considered pairing a solenoid with a small pump to ensure flow, but decided that was overkill!).

Another idea, for those technically able, is to rig up a linear actuation motor to operate the existing valve lever. That’s food for thought.

I've got one of those, although it looks suspiciously like a piece of string attached to the yellow lever. That only works for opening the valve (and doesn't do that very well). But now I know about the safety task that valve serves I shan't be using the string any more and will be removing it ASAP.

I wouldn't be confident that any actuator I could come up with, wouldn't interfere with the valve being triggered in a high-pressure situation. Others, as you say, may be more technically able that me!

Given the drive towards luxury in caravans, I can't believe that no manufacturer or accessory supplier has come up with an off the shelf solution to this. You and I can't be the only increasingly-inflexible caravanners out there.
 
Jun 16, 2020
4,819
1,940
6,935
Visit site
Sorry, didn't make clear what I meant! What I was thinking was to leave the existing valve untouched - Tee off from the pipe between the caravan water inlet and that existing valve, and take the solenoid from that Tee.

Having looked at a few solenoid valves (all of which needed approx 3 psi to ensure flow), I've modified my thoughts to tee-ing off as above, and piping from the tee to a valve in an accessible location. So the system can be drained by EITHER opening the existing valve (or it opening by itself under excess pressure), OR by opening the new valve that I've just put in on a spur. Or both, I suppose, but that seems a bit pointless!

I still like the idea of a solenoid if a usable one can be sourced, but only because I'm a gadget freak and it gives me an excuse for another switch on "the panel" (I even considered pairing a solenoid with a small pump to ensure flow, but decided that was overkill!).

Fully understood and nice and simple. Simple is often best.

But from what I have read so far, I am not convinced that all dump valves serve as a pressure relief valve. But try Googling "caravan dump valves specification" there is little to be learned. Just the Alde site thus far.

John

PS these are the actuators I had in mind.
 
Jun 16, 2020
4,819
1,940
6,935
Visit site
Just did some more research and have to agree with Prof John. In the case of Truma it appears to be set at 2.8 mb and 3.5 for Alde. I think they also have safety devices on the boilers as well.

This is my research. 1 2

I have dismissed the actuator idea. there are loads of available choices and wiring would be easy. But it would need mounting above the valve and could easily be damaged.

I have concluded that Gozzas Tee off is the way to go.

Interesting looking though, and I have learnt something new.

John
 
Mar 14, 2005
17,848
3,221
50,935
Visit site
Gonza2, I am a bit concerned after the profs post. I did not know that the dump valve is also a pressure relief valve. I tried to research this and think I have found that Truma heating have a separate Pressure release valve, but Alde use the dump valve. I can understand the concern Re heating butt can’t see a caravan pump achieving high pressures if they got left running.

Certainly something to take into consideration.
That is why it is described as a "Truma Boiler Safety Drain Valve " and not just a "drain valve".

The other clue is the design of the valve under the toggle, There is a circular section which contains a diaphragm and spring which sets the dump pressure. When you operate the lever you are lifting the diaphragm which opens the valve.

Its true that 12V submersible pumps will not generate 3.5Bar pressure, but diaphragm pumps certainly can, and will do if their pressure switch fails or has been adjusted too far.

The Truma is designed to be capable of operating with a cold water supply of up to 2.8Bar. When the Trumastore heats that 2.8Bar cold water its internal pressure can rise to about 3.5Bar, and that is why on some systems you can experience a few dribbles from the dump valve.

(Edit)
As far as the Trumastore is concerned it does not have any other active pressure relief system it has always relied on an external valve. However iit does depend on how the system has been installed. In some very early installations where it used switched taps, the user fawcets did not seal very well and the excess pressure developed whilst heating basically caused them to drip and very little pressure was retained. But as taps improved, it was necessary to include a PRV.
 
Last edited:
Nov 6, 2005
7,485
2,157
25,935
Visit site
But if you added a solenoid valve as you say, then the existing dump valve would need to be left open. Then it would not work as a pressure relief valve.

Another idea, for those technically able, is to rig up a linear actuation motor to operate the existing valve lever. That’s food for thought.

John
If the solenoid valve is in the same pipe run as the existing dump valve, then the over-pressure facility would still be present.
 
Jun 16, 2020
4,819
1,940
6,935
Visit site
That is why it is described as a "Truma Boiler Safety Drain Valve " and not just a "drain valve".

The other clue is the design of the valve under the toggle, There is a circular section which contains a diaphragm and spring which sets the dump pressure. When you operate the lever you are lifting the diaphragm which opens the valve.

Its true that 12V submersible pumps will not generate 3.5Bar pressure, but diaphragm pumps certainly can, and will do if their pressure switch fails or has been adjusted too far.

The Truma is designed to be capable of operating with a cold water supply of up to 2.8Bar. When the Trumastore heats that 2.8Bar cold water its internal pressure can rise to about 3.5Bar, and that is why on some systems you can experience a few dribbles from the dump valve.

(Edit)
As far as the Trumastore is concerned it does not have any other active pressure relief system it has always relied on an external valve. However iit does depend on how the system has been installed. In some very early installations where it used switched taps, the user fawcets did not seal very well and the excess pressure developed whilst heating basically caused them to drip and very little pressure was retained. But as taps improved, it was necessary to include a PRV.

It's extremely important and I thank you for pointing all this out. Your facts seem spot on, but I was a bit shocked to have a job finding the specifications on line. Just researching it is clear that very many of us that do not know this. I do not remember reading any of this in my vans documentation, but in one of the links I used it shows Truma explains all this but that is in an installation manual.

John
 
Jun 16, 2020
4,819
1,940
6,935
Visit site
If the solenoid valve is in the same pipe run as the existing dump valve, then the over-pressure facility would still be present.

You are correct. But at first Gonza2 was thinking of replacing that valve, as was I. But that was before we knew the truth.

The problem with the solenoid valve is finding one that's free flowing.

John
 
Mar 14, 2005
17,848
3,221
50,935
Visit site
Hi again Gozza2,

Your suggestion of adding a separate Tee piece in the cold water supply pipe is a better solution. However one of the major reasons for wanting to drain the system is to prevent frost damage to the pipes, fittings and appliances. It is very important that ALL teh water is removed, and even a few teaspoonfuls left trapped in a valve or fitting will expand as it freezes it can damage or even split the fittings.

For that reason the drain point in the system has to be at it s lowest point to prevent air locks from forming which will prevent the system from fully draining. That is one reason why the Truma valve is ideally placed at the lowest possible point in the water system. Your tee link would have to be no higher that the Truma valve, and your drain pipe must continuously fall. This begins to seem more difficult to implement, but not impossible.

I personally would avoid trying to use high tech solutions, as I know from having been involved with reliability engineering test jigs for water appliances, that low voltage solenoid valves are not very reliable, I would also be concerned about the restriction that most small solenoid valves create which would again be counter to good gravity draining performance. Keep it simple.
 
Mar 14, 2005
17,848
3,221
50,935
Visit site
It's extremely important and I thank you for pointing all this out. Your facts seem spot on, but I was a bit shocked to have a job finding the specifications on line. Just researching it is clear that very many of us that do not know this. I do not remember reading any of this in my vans documentation, but in one of the links I used it shows Truma explains all this but that is in an installation manual.

John
It is of course important that it is installed properly, and that probably why the details are in the installation instructions and not the user instructions. After all in some parts of the EU, you have to a qualified fitter to install these products, and as Damian has pointed out most manufacturers including business I have worked for have run installation training sessions for fitters.

As a user, the fact the drain valve has a double life is not really relevant, and may not be mentioned in the user instructions. - I happen to disagree, I think they should have made the point that if a discharge is seen from the dump valve when its closed, it might mean water pressure is to high and not a problem at all with the heater.
 
Jun 16, 2020
4,819
1,940
6,935
Visit site
It is of course important that it is installed properly, and that probably why the details are in the installation instructions and not the user instructions. After all in some parts of the EU, you have to a qualified fitter to install these products, and as Damian has pointed out most manufacturers including business I have worked for have run installation training sessions for fitters.

As a user, the fact the drain valve has a double life is not really relevant, and may not be mentioned in the user instructions. - I happen to disagree, I think they should have made the point that if a discharge is seen from the dump valve when its closed, it might mean water pressure is to high and not a problem at all with the heater.

Fully agree, particularly with a safety device.

John
 

TRENDING THREADS