Non return valve in air box to stop backfire damage

[ozscott]

Hi all. I have 2 V8s on LPG. 95 D1 AND 02 D2. Occasionally you get a bad lead/plug or I had a coil pack go once, and if all is not well with the spark you can get a backfire...which promptly blows the air box walls apart.

I have trialled an occy strap around the box and lid and not doing up the clips, but to get it tight enough to seal its too tight to release the pressure. I have decided to fit a non return valve or 2. The only ones that I have seen are at Whitworths marine chandlers - say the 1.5 inch ones. I havent looked at them, but presume that they are a spring loaded ball bearing. I dont know what the flow is like, but it should be good or otherwise they would restrict things too much in the marine applications.

Has anyone used something like this? Has anyone got any ideas on sourcing something like this...to be put in the lid and possible one in the side closest the radiator...

Cheers

[procrastination inc]

so you want to stop the air box being pressurised by a backfire by using a check valve?

That would close the rest of the manifold and increase the pressure even more, what would blow next?

A pressure relief valve would be in order

[ozscott]

Im not sure what you mean matey. I propose putting a non-return valve or 2 in the air box by boring holes in the air box lid and side and adding them so that in a backfire situation pressure starts to build back in the airbox (the fire coming back from the plenum and down the intake) and the valves release the pressure before the box gives way and splits and then the valves close again to stop water and contaminants getting in...

Cheers

[ozscott]

sorry mate - my original post did not make it clear where the non return valves were to be situated:)

[p38arover]

A common method is to cut a hole in the air inlet and cover it with heavy neoprene, e.g., wetsuit material which will seal it until a backfire occurs.

Also see this (scroll down page) Autogas LPG Conversion Mixers and Fittings (http://www.lpg-kits.com/mixers.htm)

[procrastination inc]

I see


I reckon they'd need to have a big area, light poppets so they can accelerate quickly and light seating springs.

how about swiss cheesing the top of the box with a 10mm drill and taping a sheet of polyethylene over the top. sacrificial explosive top :D

[procrastination inc]

snap

I was actually scoffing at the butchery of my idea, but it seems butcherous thoughts and Land Rovers go hand in hand :wasntme:

[Blknight.aus]

ok just to clariy, what your aiming at fitting is a pressure relief valve not a non return valve.

a neat way of doing this is with a dust valve which is essentialy a one way relief valve and they come premade... to fit it up its just a case of bore a hole in the filtered side of the filter, insert and secure a piece of pipe into the hole then put the dust valve on the end of the pipe...

You can see these mainly on diesels. I might be off the mark but I think the tdi and td5 intake has these one them anyway...

[ozscott]

Thanks fellas - a non-return valve is what I was going to use for a relief valve = see Whitworths Marine: Non Retun Valve 1'' - 1/ 1/2'' (http://www.whitworths.com.au/main_itemdetail.asp?item=91869&search123=non+return+valve&intAbsolutePage=3)

for example....a fuel or water non-return valve that will act as a pressure relief valve...

I wanted to make something work that didnt look like crap if I could...and I agree that it would need to get enough volume out and be lightly enough sprung to get rid of pressure before the plastic air box cracked....given that these valves are for fuel for example where they are hand primed for outboard engines, they should be lightly enough sprung, but the volume might be an issue.

Cheers

[procrastination inc]

they should be lightly enough sprung, but the volume might be an issue....

the mass of the poppet will be an issue too

I've seen PVC jobbies up to 4"

Black poly would look good

[ozscott]

Thanks Ron B - I would buy one of those if it were available in Australia. As it is I might get one imported if I cant get similar here, because that looks very good.

Cheers

[ozscott]

Thanks procrastination inc - where would I get a big PVC jobbie from mate?

[procrastination inc]

?

try reece plumbing maybe

[ozscott]

...just searching and it looks like irrigation shops stock brass and also plastic flap type non return valves around the 50mm mark - I will go and check (no pun intended) them out of the pressure needed to open them and get a couple...
Cheers all

[Blknight.aus]

http://www.emea.donaldson.com/en/compressor/support/datalibrary/049945.pdf

eyeball that and the dust vactuator valve becomes apparent.

given that they make a 4 inch version of that filter setup youd reckon you could find room for it under the hood..

[Bradtot]

Why dont you leave the hose clamps loosish..meaning just tight on the airflow meter to plenum hose, so if it backfires it blows the hose off. I do this on my Rangie and have only had one backfire in several years but it worked and saved my airflow meter.
The idea I got from the RPI website.
Brad who's been on gas since 1993:eek:

[p38arover]

I've got no idea what this look looks like as I can't access eBay: cgi.ebay.co.uk/70mm-ANTI-BACKFIRE-VALVE-LPG-CONVERSION-3-5-RANGE-ROVER_W0QQitemZ220135746141QQihZ012QQcat

See another type at the bottom of : IWEMA enterprise, LPG components (http://www.iwemalpg.com/Components.htm)

The large flat cover of the plastic LR air filter is particularly easy to modify. If you drilled, say, six large diameter holes of about 30mm dia leaving the webs between them, then you could cover these with heavy wetsuit material, e.g, a mouse pad, hinged at one end. During normal running the pad would be drawn down to seal the holes.

I'm not sure if 30mm would be too big and would allow the pad to be drawn in. One could try more smaller holes, e.g., 20mm.

With a backfire, it would be blown up to vent the pressure,

Ideally it would be better placed between the plenum chanber and the air flow sensor to avoid bacfire damage for the sensor.

One could cut a few holes in the side of the tube and cover them with wetsuit material.