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Taylors 079D Diesel Heater Improvements


Quattrodave

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Evening all,

I have diesel warm air heating & a Taylors 079D drip fed diesel heater on board.  I have the install where its has a pressurised fuel tank which you pump up and then *try* to keep at a stable pressure so it has a steady drip rate and as such a steady stable burn.... However keeping the pressure stable is a pain and as such the burn is not stable.... So I have been toying with the idea of improving the Taylors heater for some time now, looking at the manufacturers site and list of parts they have a very over priced fuel / lift pump.  Looking at it its just an old SU style pump (Google part number AZX1307) which is commonly available, same pump that was on the old mini or morris minor....  Looking at how the lift pump works it holds fuel pressure in its chamber and only uses electricity when the pressure drops. By my calculations running the hear from it it would probably only 'tick' every 45 seconds or soand as such use very little electricity.  It should also sort out keeping the fuel pressure stable and as such the burn stable.....

 

So, then my throughts moved on a little... I wondered if I could use the little dosing pump like i have on the warm air diesel heater, I'd have to run up an adjustable circuit to run it but it should be really accurate and easy to set and use...  I had an Arduino board kicking about so have spent a couple of hours prototyping my proof of concept.

 

ArduinoHeaterController2.jpg.ec88f7e5213aa9c2f9601a7f15575426.jpg

 

So essentially it works, 2 buttons increase and decrease the pulses per second minute.  Currently has a min of 30 and max of 130.  It the moment it pulses an LED but won't be difficult to drive a TIP120 or something similar to drive the fuel pump.  The 'On' pulse has a set duration of 1/4 of a second and the 'Off' duration is changed to alter the pulse rate.  If anyone is interested the Arduino code is attached....

 

More updates to follow....

Arduino Code.docx

Edited by Quattrodave
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Given the Taylors contraption expects constant pressure, I don't think a dosing pump is appropriate as it delivers a defined volume of fuel on every click. So I'd predict the downstream pressure in the pressurised fuel tank would steadily rise, or fall, depending on how accurately you manage to calibrate the number of clicks per minute to the fuel burn rate. Yes the burn rate will rise as the tank pressure rises so the thing will tend to self-balance but this may well lead to over-fueling of the Taylor contraption and therefore incomplete combustion and sooting.

 

The SU fuel pump seems a much better idea as it is a constant pressure device. Can it be calibrated though? Dave's idea of a little Arduino-controlled hammer to whack it when it stops seems an obvious solution to the known weakness in the SU design. 

 

 

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50 minutes ago, dmr said:

Arduinos are good, but those old electric SU pumps are the work of the devil.

 

Yes, I remember the 'points' in the back of them being problematic.  I was thinking about some electronic upgrade on that too... possibly an optical sensor to sense when it needs to 'fire'.

 

31 minutes ago, MtB said:

Given the Taylors contraption expects constant pressure, I don't think a dosing pump is appropriate as it delivers a defined volume of fuel on every click. So I'd predict the downstream pressure in the pressurised fuel tank would steadily rise, or fall, depending on how accurately you manage to calibrate the number of clicks per minute to the fuel burn rate.

 

I had 2 thoughts here: First i'm hoping the dosing pump would push a set amount through the 'drip' measuring device so increasing the pulse rate would increase the drip rate and the amount of fuel delivered.  Secondly, i might be able to skip the 'drip' measurement device altogether and deliver fuel directly to the burn pot.

 

I also wondndered if i can change the pulsewidth to the dosing pump (currently set to 1/4 of a second) and reduce the amount of fuel pumped for every pump... I'd guess it could be tweaked a bit...

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4 minutes ago, Quattrodave said:

I also wondndered if i can change the pulsewidth to the dosing pump

 

I'm no expert on dosing pumps but I always imagined they are a mechanical device with a spring, a solenoid, a chamber and a NRV. So each pulse of 12Vdc delivers a fixed volume of fuel regardless of the length of time of the pulse. 

 

Others here may know better....

 

 

 

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2 minutes ago, MtB said:

 

I'm no expert on dosing pumps but I always imagined they are a mechanical device with a spring, a solenoid, a chamber and a NRV. So each pulse of 12Vdc delivers a fixed volume of fuel regardless of the length of time of the pulse.

 

Agreed, but i was wondering if the pulse is reduced slightly the solenoid wouldnt have time to move as far and pump slightly less fuel....  It would be interesting to find out but not a show stopper...

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10 minutes ago, Quattrodave said:

 

Yes, I remember the 'points' in the back of them being problematic.  I was thinking about some electronic upgrade on that too... possibly an optical sensor to sense when it needs to 'fire'.

 

 

I

 

 

I think these have been available for many years, but much more fun to make your own.

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Many years ago I installed a Taylors heater on an old boat of mine. I supplied the fuel from the main fuel tank that was at a lower level than the heater. All I used was an electric in line pump. Not the SU type but the modern electronic type. The sort of thing which is available quite cheaply from somewhere like ASAP Supplies. It worked well and never gave a problem. This type of pump runs continuously and give a constant pressure. Not sure of the power consumption but probably very low.

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I take it there is no chance of getting it to run in header tank mode? Not enough height available on the boat to get the pressure required? Otherwise, that would be the obvious answer and use a float switch to turn the dosing pump on and off, or just use it as a day tank and manually refill.

What pressure is required? The Taylors web site gives no access to manuals that I could see at a quick glance.

I'd be thinking of using a pressure sensor to let the Arduino know when to turn the pump on and off. Something like this maybe. I've used them with water pressure and they can measure changes of only a few mb reliably. There are Arduino libraries already for easy interfacing. There are UK suppliers. No idea if these are compatible with diesel. This would need checking. If not, there are other pressure sensors. Measuring the actual pressure, rather than relying on a fixed pumping rate would be a much more reliable way of getting consistant pressure. You would need to work out a housing and o-ring sealing. There are industrial pressure sensors, with suitable housing, but the costs of these are high.

Alternatively, don't use the arduino at all, just a pressure switch to turn the pump on and off.

Is there air in the tank? This would act as an air spring, similar to an accumulator, or expansion tank in a boats water system and make pressure changes much slower and smoother. I am guessing this is thje way it is designed, since there is a hand pump to pressurise it. If you are not pressurising it this way, but having it entirely full of diesel, then pressure will vary a lot.  Perhaps fit an accumulator? Again, diesel compatibility would need to be checked.

Edited by Jen-in-Wellies
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  • 4 weeks later...

This weekend I have set up and tested both fuel pump types.

 

SU Diaphragm pump.

I acquired an SU Fuel pump part number AZX 1308, its a high pressure pump running at 2.7 PSI. It was connected to a take off on the main diesel tank via a filter. The out put of the pump connected directly to the taylors heater. The thermocouple and drip regulator left in place and used as normal to regulate the fuel flow. The pump works much better when physically orientated correctly, it has 'top' written on the casting. The heater works really well with this pump, it's very easy to set the required drop rate and the pressure is very stable.  As expected the pump only 'ticks' every minute or so and as such used very little electricity.  Once full of fuel the pump is surprisingly quiet!

 

Dosing pump.

I used an old 0.022ml dosing pump I had kicking around.  The arduino mentioned earlier ran the dosing pump via a TIP120 moses sat on a little heatsink. Fuel was supplied from the main diesel tank take off through a filter to the dosing pump then on to the tayors heater.  I kept the thermocouple in line but removed the drip regulator so the dosing pump was delivering fuel directly to the burn chamber.  After a little but of adjustment the system ran perfectly the faster the pump was pulsed the more fuel was delivered.  Flame control was very accurate and highly adjustable. On my setup 24 pumps per minute was a nice gentle tickover & 38 pumps per minute was a roaring inferno 😁

 

Conclusion.

Both set ups worked very well.  Neither set up I would leave running and heater alight whilst not aboard.  As far as I could measure the Dosing pump version used a little more power.  There are a number of advantages to using the dosing pump, biggest one I can think of is expansion, remote possibly bluetooth and app... The advantages of the SU pump is sheer simplicity of the system and the fact it used less power...

I have decided that the set up I will use will be the SU pump...  I hope my experiments help others out and that the 'Taylors' fuel pump is a drastically over priced SU fuel pump...!!!

Edited by Quattrodave
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The S.U. electric fuel pump is a relatively simple device, as MtB said a solenoid, diaphragm, spring and NRVs. The (crude) pulse generator (contact points) also doubles as the pressure switch. 
Initially the spring holds the diaphragm in the "out" position, the solenoid operating rod is attached and passes through the core of the solenoid, the other end being attached to the contact breakers holding them closed. When power is applied the solenoid is energised and the rod drawn in against the spring, when it reaches the end of its stroke (Suction) the contacts open and the magnetic field collapses. Spring pressure now pushes the diaphragm out delivering the fuel, when the end of the stroke is reached the contacts close and the cycle is repeated. When the fuel lines (and carburettor) are full, back pressure holds the diaphragm against the spring - holding the contacts in the open position. As fuel is drawn from the pipes the pressure will fall allowing the contacts to close for another stroke. Note there is a clever double lever device in the contacts which means that they only open or close at the stroke limits.
They were notoriously unreliable particularly when installed underneath the vehicle! Probably mostly down the damp air being drawn in around the contact points each time the pump cycled.

 

Full instructions here:-
https://www.mg-cars.org.uk/imgytr/sufuelpump.shtml

 

I would be wary of trying to control the pulse width - it would make no difference until you got it under the "pull stroke duration" , at which point, yes you reduce the solenoid stroke and thus the fuel delivered, however the contacts would not open thus the full connect/disconnect load would be on your control circuit - its quite a chunky solenoid, I'd be curious to know what the current draw is when running continuously. Your "Drip Feeder" is clearly doing the regulation and the pump responding "on demand". 

 

springy

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12 minutes ago, springy said:

The S.U. electric fuel pump is a relatively simple device, as MtB said a solenoid, diaphragm, spring and NRVs. The (crude) pulse generator (contact points) also doubles as the pressure switch. 
Initially the spring holds the diaphragm in the "out" position, the solenoid operating rod is attached and passes through the core of the solenoid, the other end being attached to the contact breakers holding them closed. When power is applied the solenoid is energised and the rod drawn in against the spring, when it reaches the end of its stroke (Suction) the contacts open and the magnetic field collapses. Spring pressure now pushes the diaphragm out delivering the fuel, when the end of the stroke is reached the contacts close and the cycle is repeated. When the fuel lines (and carburettor) are full, back pressure holds the diaphragm against the spring - holding the contacts in the open position. As fuel is drawn from the pipes the pressure will fall allowing the contacts to close for another stroke. Note there is a clever double lever device in the contacts which means that they only open or close at the stroke limits.
They were notoriously unreliable particularly when installed underneath the vehicle! Probably mostly down the damp air being drawn in around the contact points each time the pump cycled.

 

Full instructions here:-
https://www.mg-cars.org.uk/imgytr/sufuelpump.shtml

 

I would be wary of trying to control the pulse width - it would make no difference until you got it under the "pull stroke duration" , at which point, yes you reduce the solenoid stroke and thus the fuel delivered, however the contacts would not open thus the full connect/disconnect load would be on your control circuit - its quite a chunky solenoid, I'd be curious to know what the current draw is when running continuously. Your "Drip Feeder" is clearly doing the regulation and the pump responding "on demand". 

 

springy

 

I don't think he intends to control the pulse width with the SU, he will leave the pump to alter its pulse rate to suite the fuel delivery he sets on the control valve, much like the carburettor ona car. Using the SU pump keeps it simple and easy to understand.

 

Incidently as someone who did his apprenticship on Austin and the BMC cars I would not agree the pumps were as unreliable a syou imply, but certainly more unreliable than the AC mechanical pumps. However a swift whack with a spanner usually sorted them until you had a chnace to clean and adjust the contacts.

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1 hour ago, Tony Brooks said:

 

I don't think he intends to control the pulse width with the SU, he will leave the pump to alter its pulse rate to suite the fuel delivery he sets on the control valve, much like the carburettor ona car. Using the SU pump keeps it simple and easy to understand.

 

Spot on Tony.  The SU fuel pump was wired (via a switch) to the 12v dc. It's not being controlled by anything but it's own internal mechanism and pressure of the fuel in it.  @Springy explained the inner workings of the pump rather well above.

 

The dosing pump was controlled by the arduino and injected fuel directly to the burn chamber.

 

The two systems were not connected at the same time.  It was an experiment, I tried one for a few hours, took it apart and tried the other for a few hours...

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