Leaky fuel lines on CAV and lift pump... sealant?

[Tony Brooks]

34 minutes ago, Ex Brummie said:

Brake pipe fittings are flare fittings, where the pipe is opened up and held onto a cone by the retaining nut. The seal is then made by the pipe against the cone. In the oil heating industry, these are the preferred method where fittings need to be demounted regularly. There are also compression fittings that us an olive that has a flat end and the pipe is inserted into it so that once fitted, when demounted, the end of the pipe is like a bulb with a flat end. These are more prone to leaking when re-assembled.

As Tony says, correct assembly is paramount, and on such small pipes, they are very often subjected to gorilla hands on 2ft spanners and damaged in the process. The rule of thumb is to finger tight, then apply 3/4 to 1 full turn. If it leaks, then try another 1/4 turn, maybe 1/2, but if it still leaks, then start again.

 

For absolute clarity. Brake pipe flairs come in at least three types The simplest is a simple flair that looks like a tiny funnel formed on the end of the pipe. I think this is the type Ex Brummie is talking about. Then there are "flairs" that form the end of the pipe to look like a simple olive. The more modern ones start the flairing process as for the one above but then a second former is used to put a small female cone into the end of the "olive". However I don't think any flair is used with these filters.

10 hours ago, Tessy said:

Hi all,

I'm just now understanding that the leaking old union is a break pipe fitting in which presumably the pipe has been flared or shaped to form an olive at the end. So if this is the case how can it be crushed by a separate brass olive? Are they gotten with separate olives too? 

Give us a photo. I don't think I have ever seen a brake pipe flair for fitting to  a 296 filter.

[Tony Brooks]

12 hours ago, dmr said:

The new union (from Spencer and Victoria!!!!) will indeed be 5/16". As I said earlier I don't think you can get 1/2" to 8mm unions as imperial to metric unions are not readily available in all configurations.  8mm and 5/16" are pretty much mix and match, certainly if fitting a new section of pipe with a new olive.

 

I note that you have two "outs" from your filter. I expect Tony will tell me this is normal but I don't like it. Where does the second pipe go to?  The pipe between filter and lift pump is under slight vacuum, especially as the filter starts to clog, so with two pipe runs there is more potential for difficult to diagnose air leaks.

 

In a perfect world each device (engine and heater?) should have its own filter and connection to the tank.

 

................Dave

I think this is the engine filter and with DPA pumps there are three pipes. The expected inlet and outlet plus another inlet that is fed from the return from the DPA pump (see arrow heads on filter head). However at the filter end of that return pipe there is normally one way/PRV style ball valve in what looks like an oversized bolt head that the pipe union screws into. I cant see this in the OP's photos. Often the engines run well enough without this valve because the combination of lift pump and transfer pump delivers far more fuel than is required but if the lift pump lost output, there was an air leak into the system or there was a blockage I suspect the governing of engine speed may become erratic and it may be difficult to bleed properly.

[dmr]

38 minutes ago, BEngo said:

I say the compression  union approach is incorrect because  the filter head was designed for a union nut. If you look down the inlet/outlet holes the ends are tapered to fit a brazed nipple, match a formed in flare or squeeze an olive.

I went on to say you will get a satisfactory joint with a copper washer.  I didn't suggsst it was a bodge,  it isn't.  As you say, it is the modern way.  It does though rely to some extent on sealing the parallel thread in a parallel hole, which is not ideal, and on maintaining a flat face to squish the washer.

 

N

 

As long as the flat (washer) face is machined true then it should be fine, though here are rumours that some of the cheaper after-market filter heads are not well made.

I intuitively feel that the flat face will do better than the bottom of the hole with repeated re-assembly. It probably does not matter at all for most boats, I have taken my fuel system apart and put it back together so many times in the last year that I worry about stuff like this ?

 

.............Dave

[dmr]

34 minutes ago, Tony Brooks said:

I think this is the engine filter and with DPA pumps there are three pipes. The expected inlet and outlet plus another inlet that is fed from the return from the DPA pump (see arrow heads on filter head). However at the filter end of that return pipe there is normally one way/PRV style ball valve in what looks like an oversized bolt head that the pipe union screws into. I cant see this in the OP's photos. Often the engines run well enough without this valve because the combination of lift pump and transfer pump delivers far more fuel than is required but if the lift pump lost output, there was an air leak into the system or there was a blockage I suspect the governing of engine speed may become erratic and it may be difficult to bleed properly.

It looks o mounted to the boat or engine bed so I had assumed it was the first filter????

 

.................Dave

[Tony Brooks]

10 minutes ago, dmr said:

It looks o mounted to the boat or engine bed so I had assumed it was the first filter????

 

.................Dave

I have just been back to his original post and he says the same as you. I agree not the best practice because the engine might suck air back through a turned off Webasto and it makes it far too easy to run out of fuel by burning it in the Webasto.  If he has this much trouble with a simple union I would suggest he has little chance of fitting a separate take off in the tank, separate pipe, and separate filter.

[dmr]

5 minutes ago, Tony Brooks said:

I have just been back to his original post and he says the same as you. I agree not the best practice because the engine might suck air back through a turned off Webasto and it makes it far too easy to run out of fuel by burning it in the Webasto.  If he has this much trouble with a simple union I would suggest he has little chance of fitting a separate take off in the tank, separate pipe, and separate filter.

It might be wise to keep a spare blanking plug and copper washer in a handy place to quickly get the engine running again if anything does go wrong with the heater feed.

 

..............Dave

 

 

[Tessy]

Hi all, I have fitted the 5/16 union on leaky pipe with dowty and is fine now. The pipe was crushed and there was a mangled brass olive at the end of the break pipe joint instead of a flared pipe! Cut the end off and fitted new union instead.

 

now I’m interested in all the talk of webasto having its own filter. Basically there is a second filter on the engine, and this first unit with the webasto outlet used to be a sediment catcher until someone turned it into a filter as well to protect the webasto. I have a blanked off tee out of the tank that I could fit a separate webasto filter to. Why would this be necessary and how would the webasto suck fuel when off?

 

the only remaining leak is inlet to lift pump which I’m sure has the same issue as fuel filter, as the same awful boat yard installed it (I sued them over engine install previously). I’m guessing I can fix with the same type UNF adapter? I may just replace the lift pump while I’m at it as it doesn’t seem to work very well when bleeding!

Edited May 18, 2020 by Tessy

[Tony Brooks]

32 minutes ago, Tessy said:

Hi all, I have fitted the 5/16 union on leaky pipe with dowty and is fine now. The pipe was crushed and there was a mangled brass olive at the end of the break pipe joint instead of a flared pipe! Cut the end off and fitted new union instead.

 

now I’m interested in all the talk of webasto having its own filter. Basically there is a second filter on the engine, and this first unit with the webasto outlet used to be a sediment catcher until someone turned it into a filter as well to protect the webasto. I have a blanked off tee out of the tank that I could fit a separate webasto filter to. Why would this be necessary and how would the webasto suck fuel when off?

 

the only remaining leak is inlet to lift pump which I’m sure has the same issue as fuel filter, as the same awful boat yard installed it (I sued them over engine install previously). I’m guessing I can fix with the same type UNF adapter? I may just replace the lift pump while I’m at it as it doesn’t seem to work very well when bleeding!

Thanks for reporting back. " If the olive will not make a seal it has been over tightened so the pipe is crushed, the joint was not made and then removed so the olive can be inspected, the union has been cross threaded or has the wrong thread for the body  or the end of the union or the filter body has been damaged." - post #7.

 

The Webasto will not suck fuel when off but the lift pump might such air back through the Webasto when the Webasto pump is not running. If its a summer holiday boat you are not likely to run out of fuel because the Webasto has been in use for a week while iced in but it you cruise during the winter it can happen. Normally the boiler take off is a few inches higher than the engine fuel take off. Its your choice. The lower the head of fule the more  likely that air might get sucked in via the Webasto.

 

If you do fit a new pump make very sure you get the operating lever into the gap between the inner face of the crankcase and the camshaft. If you can't push the pump flange flush to the block by hand you will have the lever on the wrong side of the camshaft. If you persist in trying to bolt the pump up you will bend the lever and need another new pump.