Heater fuel starvation

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Graham_Wright

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I have installed two Planar heaters, one in the saloon and one in the aft cabin.

Their fuel supply is taken from he main fuel tank(s) after the main filter.

I have had problems with the heaters cutting out apparently due to lack of fuel. Feeding the heaters from a local can seems to fix the problem.

I have followed the installation guidelines save for using larger bore hose - 4mm instead of 2.

During my investigations I have noticed that the heat output of the heaters seems to depend on the length of the feed. As the fuel pumps are of the dosing variety, it would seem that the only control over the quantity of fuel fed is the frequency of the pump cycle. There is no (apparent) method of measuring the fuel actually entering the heater.

The pumps suck and I wonder if aeration in the fuel, insufficient to cause misfiring, may act as a "decompressing buffer". Each suck of the pump could maybe become ineffective as it would first serve to expand any air in the system. I can shift the pumps closer to the tanks thus causing them to push rather than suck.

What do others think?

(Incidentally, I have found prices ranging from £12 to £128 for pumps which look identical. As they are very simple devices, I can't see how the difference can be due to construction. Who on earth would opt to pay £128?!)
 
Graham_Wright said:
I have installed two Planar heaters, one in the saloon and one in the aft cabin.

Their fuel supply is taken from he main fuel tank(s) after the main filter.

I have had problems with the heaters cutting out apparently due to lack of fuel. Feeding the heaters from a local can seems to fix the problem.

I have followed the installation guidelines save for using larger bore hose - 4mm instead of 2.

During my investigations I have noticed that the heat output of the heaters seems to depend on the length of the feed. As the fuel pumps are of the dosing variety, it would seem that the only control over the quantity of fuel fed is the frequency of the pump cycle. There is no (apparent) method of measuring the fuel actually entering the heater.

The pumps suck and I wonder if aeration in the fuel, insufficient to cause misfiring, may act as a "decompressing buffer". Each suck of the pump could maybe become ineffective as it would first serve to expand any air in the system. I can shift the pumps closer to the tanks thus causing them to push rather than suck.

What do others think?

(Incidentally, I have found prices ranging from £12 to £128 for pumps which look identical. As they are very simple devices, I can't see how the difference can be due to construction. Who on earth would opt to pay £128?!)
Click to expand...

I think you may find that the makers say 2mm for a reason. ?
 
When I had issues with an Eberbasto, I found installing a little plastic inline filter to catch any air bubbles improved things no end and showed be where the problem was. Too many failed starting attempts made the electronics sulk.
There must be some limit on the suction that the pump will provide? Needs to be apportioned between actual head and back pressure of filters and pipework.
 
lw395 said:
When I had issues with an Eberbasto, I found installing a little plastic inline filter to catch any air bubbles improved things no end and showed be where the problem was. Too many failed starting attempts made the electronics sulk.
There must be some limit on the suction that the pump will provide? Needs to be apportioned between actual head and back pressure of filters and pipework.
Click to expand...
There should be a filter supplied with the kit but it was missing. I have ordered one.
Inline Fuel Filter and Standard Fuel Filter 6mm/8mm Glass Chrome Round | eBay

I have also ordered a pulse generator to drive the pump on the bench. I can then establish any connection between fuel line length, diameter and the ratios of suction and pressure sections.
 
The pump should be mounted close to the tank, say no more than 100cm away, and ideally close to the same level as the top of the tank. The pump should be mounted horizontally.

You should use the supplied 2mm fuel pipe. It doesn't pose a significant risk.
 
I didn't fit the supplied 2mm plastic tube and fitted 2mm bore copper piping when I installed my Chinese heater as I understood that is what should be used in marine applications. So far , touch wood, it's behaved itself, I used a dip tube directly into the main fuel tank. Using road diesel.
Also the pump should be fitted at an angle - between 30 and 45 degrees.
 
pvb said:
The pump should be mounted close to the tank, say no more than 100cm away, and ideally close to the same level as the top of the tank. The pump should be mounted horizontally.

You should use the supplied 2mm fuel pipe. It doesn't pose a significant risk.
Click to expand...
My tanks occupy the bilge keels. The feed is from pumps on the tanks tops to primary filters and then through changeover valves. There is an air trap at the point of mix.

I'll try shifting the pump to push rather than pull.
 
pvb said:
ideally close to the same level as the top of the tank.
Click to expand...
I have little experience with this type of pump but I don't understand why near the top of tank level would be preferred. I would aim to mount the pump near the tank and as low as is practicable to keep the pressure at the pump inlet as high as can be, so reducing the chance of cavitation.
 
cpedw said:
I have little experience with this type of pump but I don't understand why near the top of tank level would be preferred. I would aim to mount the pump near the tank and as low as is practicable to keep the pressure at the pump inlet as high as can be, so reducing the chance of cavitation.
Click to expand...

Because the OP has bilge keel tanks.
 
Can we establish what type of heater these are? Are they Chinese “planar” or Russian Autoterm Planar(now Autoterm air/flow). We could do woth this information first to give us an idea what the problem is. My first guess would be the fuel pipe is a problem but without any more information its hard to advise.
 
There should be an individual tank connection for each pump, let it be heater or engine or whatever. Otherwise the pump might suck air from other lines.
 
Graham_Wright said:
Chinese Planar.
Click to expand...
Ok that’s good. What you are probably seeing is a problem with the tollerances of the pumps. The pumps are not really designed to lift fuel from the tank and its particularly the case with chinese pumps where the tollerances can be somewhat slack. I had no end of trouble with chinese pumps when i fitted them for a while. They do not suck anything like as well as genuine branded pumps. They will push fuel once primed but it can run back when the heater is stopped. Increasing the bore of the pipe will make it harder to clear all the air out of the lines and make it have to run longer potentially dry when priming.
This is obviously not good. Ideally you need to run them from a tank higher than the pump. What you can do to test the pumps is dab 12V onto the pump terminals briefly repeatedly. If you remove the fuel line from the heater or pump outlet end and Pump fuel into a pot it should be 22ml per 100 clicks if its the standard chinese pump. Dont hold the 12V too long on the pump or you may burn it out.
 
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