Fuel line sizes - mixing metric / imperial ??

[Airscrew]

Hi to all.
Couple of questions.

I am planning to insert a bulb primer in my fuel line. Engine access (MD11) is very limited and bleeding single handed needs both acrobatic and contortionist skills that are dwindling..
Because of the position and routing, I will need to insert a small additional length of rubber hose.

There are two different pipes on either side of the CAV filter, one marked 5/16 (9.5mm) - the brackets are marked on the pipe. The pipe on other side of the CAV is unmarked and the OD looks slightly narrower. From the outside, they both look reinforced.

Q1. Would you put the primer bulb on the tank side, or the engine side of the CAV(primary) filter? Does it matter?

Q2. I was not able to remove the hose from either side of the CAV. Some force and twisting produced only rotation. Is there a knack to getting a hose off a barbed tail? Or do I have to cut it off?
I decided to leave it all intact yesterday and come to this forum before potentially butchering a working system!

Q3. Is the reinforcement likely to be nylon or steel. If I have to cut it, can I use a stanley knife, or will I need a hacksaw (position in situ will make this near impossible)?

Q4. The nearby chandler has 8mm and 10mm fuel hose. Can I mix 10mm and 5/16. ie put 10mm pipe onto the tail what currently has the 5/16 pipe on it?

Q5. Is there any way of telling what tail sizes are already fitted to the CAV - ofcourse before I take them off !

Thanks.

 

[PaulRainbow]

Q1. Would you put the primer bulb on the tank side, or the engine side of the CAV(primary) filter? Does it matter?

Tank side is better, this allows you to undo the bleed screw on the top of the filter housing and push the air out.

Q2. I was not able to remove the hose from either side of the CAV. Some force and twisting produced only rotation. Is there a knack to getting a hose off a barbed tail? Or do I have to cut it off?
I decided to leave it all intact yesterday and come to this forum before potentially butchering a working system!

I'd cut it with a Stanley knife.

Q3. Is the reinforcement likely to be nylon or steel. If I have to cut it, can I use a stanley knife, or will I need a hacksaw (position in situ will make this near impossible)?

Usually ok with a Stanley knife.

Q4. The nearby chandler has 8mm and 10mm fuel hose. Can I mix 10mm and 5/16. ie put 10mm pipe onto the tail what currently has the 5/16 pipe on it?

10mm should be fine on 5/16 hose tails, use decent clips.

Edit ; see posts #3 and #4

Q5. Is there any way of telling what tail sizes are already fitted to the CAV - ofcourse before I take them off !

If you don't know the type of hose or the wall thickness, you can't calculate it precisely, but measuring the OD should give you an idea.

 

[RichardS]

10mm should be fine on 5/16 hose tails, use decent clips.

Isn't 5/16th only suitable for 8mm?

I've just got back from the local motor factors with a metre of heater hose and it says 5/8th (16mm) on it and 5/8 = 10/16 so twice the OP's size.

Richard

 

[PaulRainbow]

Isn't 5/16th only suitable for 8mm?

I've just got back from the local motor factors with a metre of heater hose and it says 5/8th 16mm on it and 5/8 = 10/16 so twice the OP's size.

Richard

Yes, of course, 5/16 metric equivalent is 8mm, 3/8 equivalent is 10mm. I was taking the markings on the OPs pipe that they were 9.5mm at face value, which cannot be correct in that the pipe is both 5/16 and 9.5mm.

 

[Airscrew]

Yes, of course, 5/16 metric equivalent is 8mm, 3/8 equivalent is 10mm. I was taking the markings on the OPs pipe that they were 9.5mm at face value, which cannot be correct in that the pipe is both 5/16 and 9.5mm.

I wish I had taken a picture of the markings on the pipe.
I did the same check after posting.
5/16 cannot be 9.6mm.
And yet that is how it was marked.

Also, Having looked at CAV filters, ASAP implies they would have 8mm tails..
Hmm.

 

[PaulRainbow]

I wish I had taken a picture of the markings on the pipe.
I did the same check after posting.
5/16 cannot be 9.6mm.
And yet that is how it was marked.

Also, Having looked at CAV filters, ASAP implies they would have 8mm tails..
Hmm.

5/16 (8mm) is a common size, but 6mm, 9.5 and even 10 mm could be used. Maybe just chop the end off and then go to the chandlers for the correct size ?

 

[pvb]

Fittings for CAV filters are almost always designed for 8mm or 10mm hose.

 

[rogerthebodger]

I am currently in the process of repositioning my 3 primary CAV diesel filters/water separator (1 for each tank) and am using 8 mm pipe with both a 8 mm and 6 mm hose tails.

8 mm pipe will close down to fir my 6 mm (existing banjo fittings on the CAV filter with a worm drive clip. I use double ear clips for the 8 mm pipe on to 8 mm hose tails.

I am also fitting a bulb primer to each tank and the primary filter for each tank

 

[pvb]

8 mm pipe will close down to fir my 6 mm (existing banjo fittings on the CAV filter with a worm drive clip.

I think I'd be tempted to just swap the existing banjo fitting for 8mm tails.

 

[PaulRainbow]

8 mm pipe will close down to fir my 6 mm (existing banjo fittings on the CAV filter with a worm drive clip. I use double ear clips for the 8 mm pipe on to 8 mm hose tails.

6mm fittings are available for CAV filters.

 

[rogerthebodger]

I think I'd be tempted to just swap the existing banjo fitting for 8mm tails.

Why it not necessary the reason they are 6 mm is that the original pipe was 6 mm steel braided pipe that has a banjo fitting swagen onto the pipe.

I am away from home so don't have access to my fittings and pipe swage tooling.

 

[rogerthebodger]

6mm fittings are available for CAV filters.

Paul I have boxes and boxes of all kind of pipe fittings and have been playing with all kinds hydraulics and pneumatics for more years than I wish to remember.

The only limitation with the CAV filter is the thread in the filter head itself not the pipe size. You pick the fitting that suites the job or is the closest available that will do the job.

The required pipe size is determined by the maximum fuel flow rate in my case 8 mm is way over specified but that what I have so why change it just because several people on here think I must do it their way.

As I have said before I have spent more than enough time in Engineering to understand what is needed.

Like Frank said "I will do it my way" may be you are to young to remember.

 

[pvb]

Like Frank said "I will do it my way" may be you are to young to remember.

I guess you mean Frank Spencer.

 

[pvb]

6mm fittings are available for CAV filters.

Yes, Rogershaw seems to have some. I was simply commenting on the basis that it might be better engineering practice to use an 8mm hose tail fitting if you're going to put 8mm hose on it, rather than squeezing the hose down to seal on a smaller fitting.

 

[rogerthebodger]

I guess you mean Frank Spencer.

Yes I do remember Frank Spencer but I was another Frank much older and his real name I was thinking of

 

[rogerthebodger]

Yes, Rogershaw seems to have some. I was simply commenting on the basis that it might be better engineering practice to use an 8mm hose tail fitting if you're going to put 8mm hose on it, rather than squeezing the hose down to seal on a smaller fitting.

On yes It would be better engineering practice to use replace the 6mm with 8mm its just I cannot get 8mm where I am at the moment.

I was looking to 8 mm joining connectors but could only he 10mm so I will have to squeeze the 10mm into 8 mm pipe again not good engineering practice but its all I can get until I go home start of May back in June and I loose sailing time.

Just one of the down sides of living in to sunny climate 30 degrees C to day an 31 tomorrow

 

[PaulRainbow]

Yes, Rogershaw seems to have some. I was simply commenting on the basis that it might be better engineering practice to use an 8mm hose tail fitting if you're going to put 8mm hose on it, rather than squeezing the hose down to seal on a smaller fitting.

Yes, i was just mentioning that they were available. I personally don't like using the wrong size fittings, but as Roger is away from his stock of fittings a temporary bodge to get the job done might seem acceptable. I've no doubt he'll do it properly once he has his fittings to hand.

 

[pvb]

I personally don't like using the wrong size fittings, but as Roger is away from his stock of fittings a temporary bodge to get the job done might seem acceptable. I've no doubt he'll do it properly once he has his fittings to hand.

Yes, I'm sure you're right.

As I have said before I have spent more than enough time in Engineering to understand what is needed.