Small Diesel Shop Heater

[rcx132]

The air isn't an issue, unless the pump is drawing in that much air, the air is making it to the heater.
As long as it's just a consistent bubble at a high point in the pipe, I wouldn't worry, just think of it as damper to smooth out the fuel pulses.

I bled the hoses but saw that there was still a stream of bubbles coming out of the pump even though the hose into the pump was completely bled. I recently watched John's famous diesel heater videos on YouTube and he said that the air is being extracted from the diesel by the action of the piston. It's too much air... moving the pumps is no big deal and i get something more reliable.

 

[DAPPH]

Don't think I'd want to be on the receiving end of setting level six after last night's impressive performance on level four.

 

[m_c]

I bled the hoses but saw that there was still a stream of bubbles coming out of the pump even though the hose into the pump was completely bled. I recently watched John's famous diesel heater videos on YouTube and he said that the air is being extracted from the diesel by the action of the piston. It's too much air... moving the pumps is no big deal and i get something more reliable.

That would be a problem.
The air isn't extracted from the diesel, it's being aeriated into the diesel from a leak.
If the diesel does see enough of a vacuum to cavitate, any air in the diesel just implodes back in and visbily disappears again. If there's any air in the diesel (or any other oil) going into a pump, then that air doesn't magically permanently increase in volume because it's been briefly subjected to a vacuum. As soon as that vacuum is removed, the air goes back to the same volume it was before entering the pump (assuming the outlet pressure is the same as the input pressure).

There will be a leak somewhere, it's just not always practical to cure the leak.
The type of pipe/hose used and the hose clips often don't create a perfect seal. The nipple connections into the pumps are another source, and I'm pretty sure the internals of the pump probably are not the best designed or sealed. They'll be sealed enough to not visibly leak, but the shocking likely allows them to move and let air in.

 

[rcx132]

There will be a leak somewhere, it's just not always practical to cure the leak.
The type of pipe/hose used and the hose clips often don't create a perfect seal. The nipple connections into the pumps are another source, and I'm pretty sure the internals of the pump probably are not the best designed or sealed. They'll be sealed enough to not visibly leak, but the shocking likely allows them to move and let air in.

I've just finished moving the pumps. I put spring clips on each hose, so they're as air and fluid tight as can be. The spring clips create an even clamp force around the hose, whereas some hose clips pinch the hose and I don't trust those. There is still a steady stream of bubbles being released into the fuel but the air now goes straight up the hose to the heater without building up, so the heater is getting consistent fuel. I did notice that when the pumps were above the heaters, the metering pump frequency would change every so often as though the system was trying to adjust for the inconsistent fuel it was getting due to the air pockets.

If the diesel does see enough of a vacuum to cavitate, any air in the diesel just implodes back in and visbily disappears again.

Ok, I know nothing about this but keen to follow. There's air in diesel, do we agree on this? I just watched a YouTube video of a guy put diesel into a vacuum chamber and show this. I've also seen pro bicycle riders drawing air out of LHM oil before filling brake systems with the "air free" oil. But are you saying that's not whats causing the bubbles I'm seeing because as soon as the air is drawn out by the metering pump it would soak back in ? I don't get why it would do that? Maybe because the pump piston then re-pressurised the diesel-air to push it out the outlet ?

 

[500e]

Seen a fair few of these heaters not seen air problems after bleading

 

[m_c]

I've just finished moving the pumps. I put spring clips on each hose, so they're as air and fluid tight as can be. The spring clips create an even clamp force around the hose, whereas some hose clips pinch the hose and I don't trust those. There is still a steady stream of bubbles being released into the fuel but the air now goes straight up the hose to the heater without building up, so the heater is getting consistent fuel. I did notice that when the pumps were above the heaters, the metering pump frequency would change every so often as though the system was trying to adjust for the inconsistent fuel it was getting due to the air pockets.

Ok, I know nothing about this but keen to follow. There's air in diesel, do we agree on this? I just watched a YouTube video of a guy put diesel into a vacuum chamber and show this. I've also seen pro bicycle riders drawing air out of LHM oil before filling brake systems with the "air free" oil. But are you saying that's not whats causing the bubbles I'm seeing because as soon as the air is drawn out by the metering pump it would soak back in ? I don't get why it would do that? Maybe because the pump piston then re-pressurised the diesel-air to push it out the outlet ?

The ECUs on these are pretty basic, and don't compensate for fuelling issues. They simply spin the fan at X speed, and command the diesel pump at Y frequency.
Any change of tone is likely to be some air going through it (or the pump failing).

Basically if you have any fluid with gas in it, and you place that fluid in a vacuum (to be technically correct, decrease the pressure being applied to it), that gas will expand (Boyle's Law). If you then remove that vacuum and let the fluid return to it's original pressure, that gas will contract back to it's original volume.

The example of bike brakes you use, is using that principle to expand the gas so it forms larger bubbles and 'floats' out the fluid. It's the same reason why people use vacuum chambers for some castings/mouldings, the vacuum expands any air out the material so it's more likely to float out, then when the vacuum is removed, any air bubbles that are left, get compressed in size. Although if you manage to pull a perfect vacuum, there should be no air left.

 

[rcx132]

Seen a fair few of these heaters not seen air problems after bleading

The pumps generate bubbles, see attached pic, or this video:

(the video starts at the bit showing the bubbles).

The whole video is largely about air issues.

 

[m_c]

The pumps generate bubbles, see attached pic, or this video:

(the video starts at the bit showing the bubbles).

The whole video is largely about air issues.

View attachment 388488

Classic youtuber who doesn't understand why something is happening.

I got as far as him starting to waffle about the bigger tube absorbing the pulses, and how that's supposedly bad.
The way these heaters work, that makes no difference. The fuel passes into the gauze that surrounds the glow plug, where an air bleed then pushes the fuel through the gauze where it vaporises the fuel creating the flame. The gauze also smooths out those pulses from the pump, otherwise the flame would be very inconsistent.
If anything, a smoother delivery of fuel makes that vaporisation more consistent.

 

[rcx132]

Classic youtuber who doesn't understand why something is happening.

I got as far as him starting to waffle about the bigger tube absorbing the pulses, and how that's supposedly bad.
The way these heaters work, that makes no difference. The fuel passes into the gauze that surrounds the glow plug, where an air bleed then pushes the fuel through the gauze where it vaporises the fuel creating the flame. The gauze also smooths out those pulses from the pump, otherwise the flame would be very inconsistent.
If anything, a smoother delivery of fuel makes that vaporisation more consistent.

He's still worth watching as he's understood many parts of the heater even if he has made mistakes. As for the pulsing, maybe only the OEMs know if that's a desirable feature.

To be honest @m_c I'm not following your explanation as to why the bubbles can't be from air that was dissolved in the diesel. The pump's piston extracts the air, something I have seen just by putting oil in a syringe. Dissolving the air back into fluid is a slower process, so this air now appears as bubbles exiting the pump. It sounds consistent to me, maybe others can comment ?

Last night I also worried that my pumps and heaters are now below the fuel tank. Can fuel seep through the pump by gravity while switched off? IIRC on my Vevor heater the pump was at the side of the tank, suggesting that it won't let fuel past.

 

[Misterg]

It sounds consistent to me, maybe others can comment ?

In this context, IME, bubbles = air leak (or there is still air inside the pump that is slowly coming out).

He's calling it cavitation which is when you get vapour bubbles (not air) forming due to a drop in pressure. In that case, the bubbles disappear immediately the pressure recovers, so you wouldn't see anything in the hose coming out of the pump (there is nothing to "dissolve").

If you put anything under a vacuum, you will get the ingredients with higher vapour pressure boiling off (i.e. forming bubbles). It doesn't mean there is "air in it". The outlet hose from the heater pump is just at atmospheric pressure (not under vacuum).

Pulsing is irrelevant - all the pump is doing is delivering a known amount of fuel to a metal mesh wick were it burns off. If you've ever heard these heaters running, you can hear the flame flare up after each pump pulse (some are more noticeable than others). The heater also burns for a few seconds after the pump stops.

If there are bubbles in the fuel, the small bore hose clears them more quickly. The bigger bore hose lets bubbles build up so that if/when they do get through they can interrupt the fuel supply long enough for the heater to go out.

Eberspacher and Planar supply short lengths of rubber hose for joining the fuel line (hard plastic, small bore). This is an extremely tight fit on the fuel pump spigots and the fuel line before hose clamps, etc. are involved - No bubbles. The hose in the video above looks to be just about hanging onto the spigot on the pump.

 

[James1979]

Have mine running today, does anyone know what temp the green fuel hose is rated for?
View attachment 388511
View attachment 388512

79 degrees

 

[rcx132]

Have mine running today, does anyone know what temp the green fuel hose is rated for?
View attachment 388511
View attachment 388512

Its hard to say with these products as they don't comply with our type approvals. They often lie or don't meet our safety standards (see Border Force website). I'm keeping a close eye on my hoses.

 

[JOEPRO]

I like this idea for the exhuast to recover some of the heat

 

[Scalarocco]

I like this idea for the exhuast to recover some of the heat

I would have said that exhaust was far too restrictive. I'm sure there is a limit to the number of bends you can have.

 

[JOEPRO]

I would have said that exhaust was far too restrictive. I'm sure there is a limit to the number of bends you can have.

Yes a pipe bender would be better for the copper VS those small solder fittings.

But the principle is sound enough to recover as much heat as possible I will probably adopt something similar

 

[rcx132]

Can an extra inline fan be fitted to help air get thru the exhaust heat exchanger? And is it worthwhile for a workshop heater ? Maybe only if it's running all day.

 

[JOEPRO]

I am not looking forward to core drilling my garage masonry cavity wall.

With some 28mm copper pipe I could clip it along the wall inside and exit the exhaust through an old door frame or through the roof eaves as it should be cool enough to do so if there is say 4 - 5metres of heat extraction pipework before the exhaust point.

 

[JOEPRO]

The design of these heaters is that the combustion inlet takes fresh air from outside the "vehicle" so as to avoid any combustion fumes entering the occupied space in the event of a fault or backfire. Your setup is correct as far as that goes however if you can keep the air inlet as far away from the exhaust as possible it will ensure that the fuel air mixture is correct. If the exhaust accidently fed back into the inlet due to a breeze etc. there would be less oxygen for combustion and the efficiency will go down. probably not a big issue in this setup but worth noting for other installs.

The space heating is setup incorrectly as the heat exchanger totally isolates the combustion and the space heating. The combustion takes place inside a cast aluminium heat exchanger and the room air is passed over this finned block of aluminium. The maximum temperature of this is below 200 degrees C and more likely only 150 degrees C. You are concerned that this may be a potential ignition source if the internal room air is passed over the heat exchanger which is a healthy attitude to take. However the ignition temperature of petrol, for instance is 220C and cellulose thinners is 475C so not as big a risk as you may imagine.

As you have chosen to take cold fresh air from outside to feed the space heating it will take considerably more power (fuel) to heat the room as the temperature difference will be high to start with and will increase as the room warms. In fact the heater will end up burning fuel for no purpose. In a small space this will be negligible as the thermostat in the controller will ramp down the output. There is however another aspect that you may have missed. As you are pumping air into the space from outside to feed the space heater you must have a vent out of the space to release the same amount of air. This means having a 75mm hole in the wall to allow the heated air out so as to not restrict the airflow over the heat exchanger. This vent should be as low down the wall as possible so that the coldest air in the room is vented first. For this example I have assumed that the doors and windows are well sealed but in reality there may be plenty of natural ventilation to preclude the need for a vent to outside.

I'll get of my lectern now and say its up to the installer to decide what is and isn't safe and it's up to physics to tell you what is and isn't efficient
On my install I've mounted my heater up near the ceiling with an extended vent pointed down which is possibly the worst way to install it but I had no floor space where I could fit it so it is what it is. I have also extended the exhaust along the internal wall and fitted radiator plates on it to gain as much heat output that I can. I used 22mm copper pipe which amazingly was the cheapest way to do it and was a great fit onto the existing exhaust. The radiator plates are some Alu plate attached with 22mm copper pipe clips and it's all painted VHT matt black. It is surprisingly efficient and I can see 180 C at the exhaust reducing down to 40 C where it goes through the wall. It's less than 3m and a straight pipe so does not restrict the exhaust. Because of the length I don't need the silencer (they don't do much anyway) but if I did I would put it at the far end outside the workshop which is 54 square metres BTW.

Can you share photos of your setup please and exhaust?

It sounds very good to me

 

[500e]

Have posted on exhaust heat recovery before.
Would think that pipe would restrict the ex and cause carbon build up, also it has to vent outside. You could die.
Have had a hand in 5 my suggestion is at least 2mtrs of 100/150mm pipe angled down or you will have condensate problem, the thicker the pipe the better for heat retention.
Mains psu's are not good, switch off they stop mains fail they stop it will shorten the life and cause carbon build up, if you run like @fizzy flat out for extended periods OK.
Have done 2 with the big exhaust works well, one with an 8Mtr run

 

[fizzy]

Have posted on exhaust heat recovery before.
Would think that pipe would restrict the ex and cause carbon build up, also it has to vent outside. You could die.
Have had a hand in 5 my suggestion is at least 2mtrs of 100/150mm pipe angled down or you will have condensate problem, the thicker the pipe the better for heat retention.
Mains psu's are not good, switch off they stop mains fail they stop it will shorten the life and cause carbon build up, if you run like @fizzy flat out for extended periods OK.
Have done 2 with the big exhaust works well, one with an 8Mtr run

There really is no need to worry about the odd powercut. My heaters are often switched off without proper shut down procedures. Or were until I pointed put the error of their ways! One of my heaters ran for over 5000 hours with no problems at all. Until I was ill in hospital and a well meaning mate of mine filled the fuel tank with bleach instead of kero