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

[Tessy]

I have just replaced my CAV filter unit as the old one was cross threaded and somewhat leaky. I replaced the unions on the leaky hoses (the outlets to engine and webasto), these are now dry. However the inlet from the diesel tank, which is 8mm copper pipe and with the original union, is now leaking! I will replace this union with a new compression fitting, but has anyone used a diesel and metal-friendly thread sealant like Locktite 577 on these fuel installations? I am sick of leaks and I want to make sure the seal is good. However I am concerned that if I use the stuff on the thread that goes into the filter body, the unit will then need to be replaced if it doesn't work (because the female thread will be gunked up with sealant!) Is this a reasonable concern? Also, is there any sense to smearing a bit of locktite over the olive too, prior to compression? Will it set like that?

 

Incidentally, my fuel lift pump is also leaking (I THINK form the inlet union but perhaps the pump itself is kaput). Same question with regards the internal thread of the lift pump! 

 

With all this diesel collecting I may shut off the supply, but wouldn't I then get air in the system which would need to be bled anyway? 

 

engine is a BMC 1.8

[BEngo]

Sealant:  Heldite.

Or the blue stuff from Screwfix.

No need to put anything on olives.  They will seal fine if they are properly tightened. Start with a new one.  Nut finger tight, then one full turn only.

Have a careful look at the fuel pump inlet.  It may have a crack caused by over enthusiastic tightening to stop a leak.

 

If there is sealant in a female thread, clean it out with a tap of the right size.  Some filters are UNF, which is easily cross threaded, some are BSP.

 

Shutting off the system may mean air, but it may bleed out before it affects the fuel pump and injectors.  You cannot tell till you try.  Changing fittings etc. certainly means you should bleed the system.

N

[dmr]

52 minutes ago, BEngo said:

Sealant:  Heldite.

Or the blue stuff from Screwfix.

No need to put anything on olives.  They will seal fine if they are properly tightened. Start with a new one.  Nut finger tight, then one full turn only.

Have a careful look at the fuel pump inlet.  It may have a crack caused by over enthusiastic tightening to stop a leak.

 

If there is sealant in a female thread, clean it out with a tap of the right size.  Some filters are UNF, which is easily cross threaded, some are BSP.

 

Shutting off the system  may mean air, but it may bleed out before it affects the fuel pump and injectors.  You cannot tell till you try.  Changing fittings etc. certainly means you should bleed the system.

N

Ive been struggling with a suspected air leak recently. If diesel is leaking out then air is almost certainly leaking in if its on the suction side.

The common CAV filter heads do have two threads, some are UNF but others are metric. Sometimes the unions seal on the seat at the bottom of the threaded hole, whilst others use a copper washer on the machined face. On our boat the connections to the fuel cock were BSP parallel without any sealing face, just done up with PTFE tape, which is a potential leak.

 

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

[Tessy]

3 hours ago, BEngo said:

Sealant:  Heldite.

Or the blue stuff from Screwfix.

No need to put anything on olives.  They will seal fine if they are properly tightened. Start with a new one.  Nut finger tight, then one full turn only.

Have a careful look at the fuel pump inlet.  It may have a crack caused by over enthusiastic tightening to stop a leak.

 

If there is sealant in a female thread, clean it out with a tap of the right size.  Some filters are UNF, which is easily cross threaded, some are BSP.

 

Shutting off the system may mean air, but it may bleed out before it affects the fuel pump and injectors.  You cannot tell till you try.  Changing fittings etc. certainly means you should bleed the system.

N

Thanks! Can you explain the difference between BSP and UNF threads? The unit is UNF. I have a new UNF union for it but the compression end of it is 5/16 while the pipe itself is 8mm!! I do have 8mm compression unions too, but their threads are BSP! What can I do here? Perhaps use the UNF union with the nut and olive from the 8mm one so the pipe fits??

[Tony Brooks]

40 minutes ago, Tessy said:

Thanks! Can you explain the difference between BSP and UNF threads? The unit is UNF. I have a new UNF union for it but the compression end of it is 5/16 while the pipe itself is 8mm!! I do have 8mm compression unions too, but their threads are BSP! What can I do here? Perhaps use the UNF union with the nut and olive from the 8mm one so the pipe fits??

The difference is thread pitch (threads per inch - UNF has more) and shape of the threads. I am a bit mystified about what you actually have. The CAV filters use a special union "bolt" with a hexagon at one end and a taper to compress the olive at the other. The olives are the same for both UNF and BSP unions as long as the pipe size is correct. Use the union "bolt" with the same thread as the filter and I suspect the 5/16 olive will fit and seal. If not then probably any 8mm olive would work but probably a double tapered brass olive would be better than  a parallel copper one.

[Tessy]

47 minutes ago, Tony Brooks said:

The difference is thread pitch (threads per inch - UNF has more) and shape of the threads. I am a bit mystified about what you actually have. The CAV filters use a special union "bolt" with a hexagon at one end and a taper to compress the olive at the other. The olives are the same for both UNF and BSP unions as long as the pipe size is correct. Use the union "bolt" with the same thread as the filter and I suspect the 5/16 olive will fit and seal. If not then probably any 8mm olive would work but probably a double tapered brass olive would be better than  a parallel copper one.

Tony, what I have is 8mm copper pipe for main fuel line. I need to connect it to the CAV which has UNF thread. however the union bolt I have for it is made for 5/16 pipe, not 8mm. Since this is slightly smaller, I am concerned that the 8mm pipe will not fit through the hole in the compression nut. Now, I do have some 8mm union bolts too, but these have BSP threads. I am guessing that I can't just use the compression nut from the latter on the former?

 

An easier thing to try is to leave the existing union on the pipe, remove it to change the olive and pop some loctite 577 on the thread entering the CAV, but my concern is that if this doesnt work I will be left with a CAV that is gummed up with loctite. 

[Tony Brooks]

9 minutes ago, Tessy said:

Tony, what I have is 8mm copper pipe for main fuel line. I need to connect it to the CAV which has UNF thread. however the union bolt I have for it is made for 5/16 pipe, not 8mm. Since this is slightly smaller, I am concerned that the 8mm pipe will not fit through the hole in the compression nut. Now, I do have some 8mm union bolts too, but these have BSP threads. I am guessing that I can't just use the compression nut from the latter on the former?

 

An easier thing to try is to leave the existing union on the pipe, remove it to change the olive and pop some loctite 577 on the thread entering the CAV, but my concern is that if this doesnt work I will be left with a CAV that is gummed up with loctite. 

Have you tried the pipe in the union? I suspect it will and if not an 8mm drill will probably solve the issue.

 

You can not put a UNF bolt intp a BSP hole or a BSP bolt into a UNF hole. the threads are totally different.

 

It is the olive that creates the seal to the pipe, nut & housing so if it wont seal dry (well maybe with a smear of grease) I don't see how sealer is anything other than a bodge that may or may not work. Check the pipe won't fit through the nut, it it does not I would drill the union bolt so it does. Then use a new 8mm olive.

 

To repeat - the threaded portion of that type of union takes no part in sealing the joint. 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.

 

 

[dmr]

8mm and 5/16 are very close. If you buy an 8mm olive it likely comes out of the same box as the 5/16. The difference in pipe diameters is probably less than the manufacturing tolerance.

 

I think 5/16 copper pipe usually has a thicker wall so 8mm might not meet the "letter of the law" of some boaty regulation or other.

 

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

[Tony Brooks]

26 minutes ago, dmr said:

8mm and 5/16 are very close. If you buy an 8mm olive it likely comes out of the same box as the 5/16. The difference in pipe diameters is probably less than the manufacturing tolerance.

 

I think 5/16 copper pipe usually has a thicker wall so 8mm might not meet the "letter of the law" of some boaty regulation or other.

 

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

and may well be easier to crush under an overtightened olive.

[BEngo]

Please can we have some pictures of the fuel filter inlet and the fitting you want to put into it?

A 5/16 fitting will usually accept an 8mm pipe, provided you use an 8mm olive.  If not enlarge the hole in the nut and the recess in the fitting with an 8mm drill.

 

As said a ove by Tony though,  the filter is meant to be used with a union nut.  This is a longish male thread with a hexagon at one end and a hole through of pipe size.  The non hexagon end is shaped to form an olive, assisted by the shape of the filter housing, or will  push a nipple brazed on the end of the pipe into  the housing.  In either case the seal is the olive or nipple against the housing.  The thread is only there to provide the push.

https://www.google.com/aclk?sa=l&ai=DChcSEwjyoZSezbjpAhWLse0KHdwzDJ0YABAEGgJkZw&sig=AOD64_16_SwqPDiJREw8gfsI-KrONfqPww&ctype=5&q=&ved=2ahUKEwj80ImezbjpAhUbSxUIHZ-FAwQQwg96BAgKEBE&adurl=

 

Do not worry about a bit of sealant in the female tthread.If you have no tap,  in the worst case you can always scrape it out with a bit of bent wire or the bent end of a scriber.

N

 

Edited May 16, 2020 by BEngo
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[dmr]

Or, if your filter head is like mine it also has a machined face on each port so you could get a 1/2" UNF to 8mm fitting and seal it with a copper washer.

You will probably have to get a 1/2" to 5/16 as metric-imperial conversions can be hard to get, a bit like the Brexit negotiations  ?

 

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

[Tessy]

3 hours ago, BEngo said:

Please can we have some pictures of the fuel filter inlet and the fitting you want to put into it?

A 5/16 fitting will usually accept an 8mm pipe, provided you use an 8mm olive.  If not enlarge the hole in the nut and the recess in the fitting with an 8mm drill.

 

As said a ove by Tony though,  the filter is meant to be used with a union nut.  This is a longish male thread with a hexagon at one end and a hole through of pipe size.  The non hexagon end is shaped to form an olive, assisted by the shape of the filter housing, or will  push a nipple brazed on the end of the pipe into  the housing.  In either case the seal is the olive or nipple against the housing.  The thread is only there to provide the push.

https://www.google.com/aclk?sa=l&ai=DChcSEwjyoZSezbjpAhWLse0KHdwzDJ0YABAEGgJkZw&sig=AOD64_16_SwqPDiJREw8gfsI-KrONfqPww&ctype=5&q=&ved=2ahUKEwj80ImezbjpAhUbSxUIHZ-FAwQQwg96BAgKEBE&adurl=

 

Do not worry about a bit of sealant in the female tthread.If you have no tap,  in the worst case you can always scrape it out with a bit of bent wire or the bent end of a scriber.

N

 

Here are a few pictures to clarify. One pic of the new UNF union I want to use. One pic of this type union already installed on one side of the unit, and another pic of 8mm leaky inlet using old union. I want to replace this old union with new type but it is for 5/16 pipe, not 8mm like is there. 

[Tony Brooks]

The thread in the filter and the thread on the union are both parallel so it should go right in and seal with a soft washer on the face of the filter and the face on the land at the end of the thread on the union as DMR has alreday explained. No sealer should be required but if you must try to seal it then I would suggest a little liquid PTFE only on the thread or even PTFE tape, possibly gas tape but whatever you do do not let the tape hang over the end of union in case it sheds into the fuel system. However the filter should catch any that does.

 

I still think something is wrong if the original fitting will not seal, as I said probably a crushed pipe.

[dmr]

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

[BEngo]

The top picture is the incorrect fitting.  You can make a satisfactory job using it if you fit a copper or fuel proof fibre washer between the fitting and the filter housing.

The second picture  is the proper fitting.  If it is leaking the pipe olive is the wrong size  or has crushed the pipe, or is otherwise incorrectly assembled; probably the pipe is not pushed in far enough before tightening.

 

The third picure  fitting needs a copper or fibre washer on the male thread end to make a seal.

[Ex Brummie]

A crushed pipe is most likely as your 8mm will be soft copper. If the original olive was brass, it is easy for thepipe to get crushed or necked, and a new olive will not take up the imperfections. A copper olive is much more reliable on soft copper. If you have taken the olive up and it is tight on the pipe, then a 2 or 3 turns of ptfe tape round the olive may seal it. This method is used often on oil Aga's where a6 monthly service involves the demounting of compression fittings. There is no real pressure to contend with.

[dmr]

4 minutes ago, BEngo said:

The top picture is the incorrect fitting.  You can make a satisfactory job using it if you fit a copper or fuel proof fibre washer between the fitting and the filter housing.

The second picture  is the proper fitting.  If it is leaking the pipe olive is the wrong size  or has crushed the pipe, or is otherwise incorrectly assembled; probably the pipe is not pushed in far enough before tightening.

 

The third picure  fitting needs a copper or fibre washer on the male thread end to make a seal.

Why do you say this? (you might be correct, you usually are). With my limited experience I would say the union and copper washer is the modern way of doing it, whilst the "brake pipe" style fitting is the older way. I expect the brake pipe style is also cheaper which is why its common in automotive applications.

 

I note that suppliers of filter heads (ASAP etc) invariably list the unions as additional items.

 

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

[dmr]

5 minutes ago, Ex Brummie said:

A crushed pipe is most likely as your 8mm will be soft copper. If the original olive was brass, it is easy for thepipe to get crushed or necked, and a new olive will not take up the imperfections. A copper olive is much more reliable on soft copper. If you have taken the olive up and it is tight on the pipe, then a 2 or 3 turns of ptfe tape round the olive may seal it. This method is used often on oil Aga's where a6 monthly service involves the demounting of compression fittings. There is no real pressure to contend with.

 

There appears to be some debate about this. I recently looked at lots of plumbing forums to help decide if I should use copper or brass olives. A few people said copper for a once only fitting, but brass if the fitting is to be undone and re-fitted......but never believe everything you read on a forum ?

 

 I too have seen significant necking from brass olives.

 

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

[Tessy]

1 hour ago, dmr said:

 

There appears to be some debate about this. I recently looked at lots of plumbing forums to help decide if I should use copper or brass olives. A few people said copper for a once only fitting, but brass if the fitting is to be undone and re-fitted......but never believe everything you read on a forum ?

 

 I too have seen significant necking from brass olives.

 

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

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? 

[dmr]

22 minutes 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? 

 

I believe posters here are talking about a standard compression fitting where the pipe could be crushed by the olive by excessive tightening, no problem with normal tightening. I much prefer to use standard compression fittings plus the union as in your first photo. BEngo looks to prefer the brake pipe style fittings and he knows his stuff so lets wait for his reply.

 

One of my reasons is that the filter heads are aluminium, a soft metal, so the threads and internal seat are vulnerable, so I prefer to use a union which could be replaced if required. It also makes it easier to cobble together alternative piping in an emergency. It is an additional joint and so source of leakage but a copper washer seal to a machined face is pretty damn good.

 

(i've got unions on the first filter and brake pipe fittings on the second ?)

 

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

Edited May 16, 2020 by dmr
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[Tony Brooks]

Brake pipe fittings use an "olive" that is formed from and on the end of the pipe. The CAV filter unions use a separate olive on the pipe although they look superficially similar and I think some actually crush the end of the fitting onto the pipe to form the seal. What is common on both fittings is that they shoudl both seal without any sealer if correctly assembled.

[Ex Brummie]

1 hour ago, Tony Brooks said:

Brake pipe fittings use an "olive" that is formed from and on the end of the pipe. The CAV filter unions use a separate olive on the pipe although they look superficially similar and I think some actually crush the end of the fitting onto the pipe to form the seal. What is common on both fittings is that they shoudl both seal without any sealer if correctly assembled.

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.

[Tacet]

Apologies for hijacking this thread - I would like to put a 296 type filter into a heating oil line.  At the moment there is a really tiny filter at the joining of a 3/8 copper to 10mm plastic (underground) pipe.

 

Is there is a BSP filter head?  I can't find a 1/2 UNF male to 10mm compression fitting.

 

 

 

 

[Tony Brooks]

8 minutes ago, Tacet said:

Apologies for hijacking this thread - I would like to put a 296 type filter into a heating oil line.  At the moment there is a really tiny filter at the joining of a 3/8 copper to 10mm plastic (underground) pipe.

 

Is there is a BSP filter head?  I can't find a 1/2 UNF male to 10mm compression fitting.

 

 

How is the 10mm pipe fitted into the existing filter head? if its a separate screw in compression fitting it may fit the 296.I think you cam get BSP 296 filter heads, ask your local diesel equipment specialist.

[BEngo]

12 hours ago, dmr said:

Why do you say this? (you might be correct, you usually are). With my limited experience I would say the union and copper washer is the modern way of doing it, whilst the "brake pipe" style fitting is the older way. I expect the brake pipe style is also cheaper which is why its common in automotive applications.

 

I note that suppliers of filter heads (ASAP etc) invariably list the unions as additional items.

 

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

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