Diesel heater fuel supply from CAV filter

[samfieldhouse]

Fitted my Autoterm 2D yesterday and it's running nicely - currently 22oC on board!
We've taken the fuel supply from the engine CAV filter/water separator (via a stop cock), an idea mostly inspired by various posts on the subject on this forum (thanks all!).

Mine is tapped, like you suggest, after the filter. Have not used it much so can't say it is the right way, but is was the factory way and I see no problems with it. You'd definitely want it filtered and it would be a pain to install another filter unit just for that.

Put it on the filter but would suggest putting a stop cock in line for maintenance

I have done two installations both worked for years without problems...the other from one of the spare outlets from the CAV filter.

It would be preferable to take the feed from the CAV filter

I took the feed from the second outlet on the engine filter

My Eberspacher, professionally installed 15 years ago, is connected to a spare outlet on the primary fuel filter and there have been no problems as a result.

However, a chappy in my club is really convinced that the engine pump (Yammer 2GM) will pull fuel back from the heater fuel pipe via the filter, instead of drawing from the tank. Something about the pump's non-return valve being overcome by the suction from the engine.

I got an F in my physics GCSE, apparently it doesn't stand for 'fabulous', so I'm not really qualified on the varying degrees of pump suckiness, but my assumption is that it's easier to pull from the tank via the filter than against another pump?

Od course this is easily settled by running the engine and the heater at the same time, but I'm interested to know where this (mis?)information has come from, and if it's possible that this could cause a theoretical problem?

 

[PaulRainbow]

Fitted my Autoterm 2D yesterday and it's running nicely - currently 22oC on board!
We've taken the fuel supply from the engine CAV filter/water separator (via a stop cock), an idea mostly inspired by various posts on the subject on this forum (thanks all!).













However, a chappy in my club is really convinced that the engine pump (Yammer 2GM) will pull fuel back from the heater fuel pipe via the filter, instead of drawing from the tank. Something about the pump's non-return valve being overcome by the suction from the engine.

I got an F in my physics GCSE, apparently it doesn't stand for 'fabulous', so I'm not really qualified on the varying degrees of pump suckiness, but my assumption is that it's easier to pull from the tank via the filter than against another pump?

Od course this is easily settled by running the engine and the heater at the same time, but I'm interested to know where this (mis?)information has come from, and if it's possible that this could cause a theoretical problem?

He's talking rubbish, simple.

 

[billyfish]

Mine works fine

 

[B27]

On the other hand, both engine and heater systems are a pain in the neck if any air gets it, so keeping the two independent has some appeal to it.
A little filter for the heater is a couple of quid.
An independent take-off from the tank is the bigger problem.
Eber definitely used to recommend it though, they sold a stand-pipe which could be fitted from outside the tank IIRC?

 

[pyrojames]

I run mine of the CAV (soon to be racor..). I do have a separate isolation valve on the heater circuit though.

 

[ChromeDome]

I run my 2 Webastos directly off the tank, not though other than their own filters, as suggested by the installation manual.

 

[Sandy]

I just ran the tube from the secondary fuel line at the tank. Risking an air leak in the line feeding the engine is one risk you don't need to take.

The rest of the world is more than happy with unfiltered fuel for this use.

 

[Pye_End]

However, a chappy in my club is really convinced that the engine pump (Yammer 2GM) will pull fuel back from the heater fuel pipe via the filter, instead of drawing from the tank. Something about the pump's non-return valve being overcome by the suction from the engine.

The fuel will take the path of least resistance. For the engine to draw back fuel from the heater then the fuel must be replaced by something ie air. Perhaps it might be possible for the engine pump to have enough grunt if the CAV to tank line is blanked off, I don't know, but whilst it can easily get fuel from this route there is going to be very little 'suck' along to the heater. Given the number of applications which are piped up from the CAV (including mine) then it sounds as though this might be a potential theory that is not bourne out by practice.

When mine was (professionally) fitted, the installers remarked that they were not supposed to pipe it from the CAV, but from their experience it was not an issue, so they did it anyway. Quite who had required this of them I do not know, but presumably the manufacturer of the heater.

 

[fredrussell]

I suppose you could argue that if you connect heater to engine’s filter you could run the tank dry with the heater, whereas a tank standpipe can be made to a length that always leaves a few inches of fuel in the tank. You would have to be a silly sod to run your fuel low enough that the heater might finish it off though.

 

[Refueler]

When I get round to fitting my Vevor unit - I will use the separate tank supplied .... I'm never too happy having all of one supply ...

I know many people use the filter as supply point ... but I'm not so happy to do it ... knowing me - I'll end up with no engine and no heater !!

 

[Ammonite]

I fitted a NRV between the CAV and the heater but this was due to potential air leaks given that the fuel line connections of most heaters dont immediately inspire a lot of confidence (plastic pipes stuffed into rubber tube etc). In practice I doubt it was necessary

 

[vyv_cox]

The pump for all of the heaters I am aware of is a tick-tick type, which means it is positive displacement giving a measured charge on each tick. Positive displacement pumps are their own NRV, back flow through them is impossible.

I did not take the heater supply for my Eberspacher from the filter, I took it from a T downstream of it. Engine and heater have run perfectly since installation, sometimes simultaneously, for the past 25 years.

 

[rogerthebodger]

The pump for all of the heaters I am aware of is a tick-tick type, which means it is positive displacement giving a measured charge on each tick. Positive displacement pumps are their own NRV, back flow through them is impossible.

If you mean the type of fuel pump below is not a true positive positive pump as the piston acts under spring thus the outlet is limited to the pressure excerpted by the spring. so it's more akin to a diaphragm pump which do have NRV on the inlet and outlet so will not allow any backflow as the OP wishes to install

 

[Refueler]

I assumed they were a Solenoid type action ... giving rise to the TICK TICK ...

 

[vyv_cox]

If you mean the type of fuel pump below is not a true positive positive pump as the piston acts under spring thus the outlet is limited to the pressure excerpted by the spring. so it's more akin to a diaphragm pump which do have NRV on the inlet and outlet so will not allow any backflow as the OP wishes to install

The heater pumps I am aware of are diaphragm pumps. I do not recognise that one.

 

[rogerthebodger]

The heater pumps I am aware of are diaphragm pumps. I do not recognise that one.

Can you provide a link to the one you are aware of

 

[vyv_cox]

I assumed they were a Solenoid type action ... giving rise to the TICK TICK ...

If it's a tick-tick it has to be positive displacement. Centrifugal is the alternative, continuous drive.

 

[rogerthebodger]

If it's a tick-tick it has to be positive displacement. Centrifugal is the alternative, continuous drive.

No the solenoid type as I posted has a solenoid the causes the diaphragm to suck the fuel into the pump chamber (diaphragm and a spring then pushes the fuel out to deliver it to the fuel injector pump or carburetor as in the old SU type fuel pump

Electric fuel diaphragm pump

An engine mechanical lift pump also works in a similar way

A positive displacement pump can be diaphragm type or a gear type as in an lubrication oil pump will give a set flow depending on the speed of the pump operation.

The pumps shown above will give a flow up to the set pressure et by the spring return force so once the pressure at the outlet exceeds the set pressure no more fuel will be pumped as the solenoid or pump lever will stop operating so no more flow.

A diaphragm pump like the Henderson Mk V is a positive displacement as there is no spring preventing the diaphragm from operating once a set pressure is reached.

I had an electric Mk V pump blow off my head outlet pipe from the skin fitting because the seacock was closed and the pressure built up to such an extent the the pipe could not stand the pressure so something had to give

Hydraulic systems generally have a pressure release valve to prevent overpressure as does boat hot water tanks

There are lots of different types of liquid pumps.

My boat steering is hydraulic and uses a axial piston pump that has a variable piston stroke by using an adjustable swashplate and can be fitted with a pressure compensated automatic adjustment that will operate in the same way as the spring diaphragm pump shown above

 

[Refueler]

Gor blimey guys ....

And there was me looking at what is basically a tube with connectors ... thinking that the TICK TICK was the solenoid pin hitting stops up / down as it acted like a piston ..

Oh well ...

 

[vyv_cox]

No the solenoid type as I posted has a solenoid the causes the diaphragm to suck the fuel into the pump chamber (diaphragm and a spring then pushes the fuel out to deliver it to the fuel injector pump or carburetor as in the old SU type fuel pump

Electric fuel diaphragm pump

An engine mechanical lift pump also works in a similar way

A positive displacement pump can be diaphragm type or a gear type as in an lubrication oil pump will give a set flow depending on the speed of the pump operation.

The pumps shown above will give a flow up to the set pressure et by the spring return force so once the pressure at the outlet exceeds the set pressure no more fuel will be pumped as the solenoid or pump lever will stop operating so no more flow.

A diaphragm pump like the Henderson Mk V is a positive displacement as there is no spring preventing the diaphragm from operating once a set pressure is reached.

I had an electric Mk V pump blow off my head outlet pipe from the skin fitting because the seacock was closed and the pressure built up to such an extent the the pipe could not stand the pressure so something had to give

Hydraulic systems generally have a pressure release valve to prevent overpressure as does boat hot water tanks

There are lots of different types of liquid pumps.

My boat steering is hydraulic and uses a axial piston pump that has a variable piston stroke by using an adjustable swashplate and can be fitted with a pressure compensated automatic adjustment that will operate in the same way as the spring diaphragm pump shown above

Both your pump types have valves. Which as I said act as their own nrvs. Not sure what you are arguing about.