Inertia cut off switch

[Jonny-Jimbo]

Hi all,

I'm putting a low pressure electric pump on my Vitesse as I'm fed up of the appalling quality of the mechanical pumps available these days (I fitted three new ones in succession and all of the leaked like a sieve). Anyway, although I have no intention of shunting the Vitesse, I want the security of an inertia cut of switch to be fitted. Can anyone tell me what they have fitted in terms of junk yard parts etc?

I'm hoping for something I can fit in the engine bay near the pump, preferably with only two or three wires.

What is anyone's suggestion?

If it matters, the pump I'm fitting is a a modern version of the SU pump as fitted to old Mini's etc. The supply rate and pressure is suitable for the carbs and engine tune.

[oil_on_the_carpet]

All much of a muchness.

http://chinn.blogspot.co.uk/2005_12_01_archive.html

http://www.ebay.co.uk/sch/i.html?_sacat=0&_sop=15&_nkw=fuel+inertia+switch&_frs=1

[John Bonnett]

I fitted one from a Fiesta and managed to get one complete with mating plug.

[TedTaylor]

A switch is not so critical with low pressure (such as SU) pumps, after all cars ran for decades without them. and often a leak was an inconvenience and not necessarily a major hazard.

However it is essential for high pressure (Triumph PI systems) and also for modern 'medium' pressure ones.  With high/medium pressure the fuel sprays around in an atomised state and it does not take much to trigger a fire.

Mind you with my Mk1 PI estate there is no inertia switch fitted as standard though I will be putting one into the system in an unobtrusive position.

MUT

[JohnD]

The one that Jason (Chinn) suggests is used by a ridiculously wide range of manufacturers, so it must be good, and cheap.
As John (Bonnet) says, make sure to get one WITH the connection plug to the loom, else it's a b*gg*r to fit.
And, there are two types, with two and three terminals.    The latter sets off a warning light to tell you that it's tripped - many will say it's an idiot light, how could you not know,  but when so many other things can stop a classic, suddenly ....
I kicked myself when running a kerb tripped it and even though I'd mounted it within reach on the dash, where I could reset it, I assumed a host of other causes.

John

[Steve AKA vitessesteve]

See http://vitessesteve.co.uk/PI_Project/Inertia%20switch for some thoughts I had about this matter.

[oil_on_the_carpet]

Quoted from TedTaylor

A switch is not so critical with low pressure (such as SU) pumps, after all cars ran for decades without them. and often a leak was an inconvenience and not necessarily a major hazard.

However it is essential for high pressure (Triumph PI systems) and also for modern 'medium' pressure ones.  With high/medium pressure the fuel sprays around in an atomised state and it does not take much to trigger a fire.

Mind you with my Mk1 PI estate there is no inertia switch fitted as standard though I will be putting one into the system in an unobtrusive position.

MUT

With any electric fuel pump, not fitting an inertia switch is stupid unless you really fancy the thought of your fuel pump pumping gallons of petrol over your hot engine after a crash.

[TedTaylor]

Quoted from oil_on_the_carpet

With any electric fuel pump, not fitting an inertia switch is stupid unless you really fancy the thought of your fuel pump pumping gallons of petrol over your hot engine after a crash.

Wonder how all those cars back to the 1930s which were fitted with SU fuel pumps - including high performance cars like Jags etc. in the 1950s and 1960s - coped.  And of course rally cars in the 1960s and 1970s fitted with the higher output SU fuel pumps.  Perhaps it was not rust that killed cars off but them repeatedly going up in flames and no one noticed.

My comment was for inertia switches on low output pumps not being so critical as history has proven.

NUT

[Nick Jones]

Cars catching fire after accidents seems to be less common than it once was  (even if cars randomly catching fires seems more common!) which may be related.

Personally I really don't fancy a fuel pump of any pressure keeping going in a crashed car and fitting an inertia switch to prevent seems like a no-brainer.  It's not even hard or expensive to do.

Nick

[Richard B]

As Ted say's with a PI spraying petrol at a 110psi an inertia switch is highly disirable.

John, I had the same problem in my Spitfire, the pump was tripped out on the way to SEM and I had totally forgotten about the inertia switch  

[JohnD]

I am NOT arguing that an inertia switch is a bad idea, but can a hot engine ignite spilt petrol?

It's known and been demonstrated that a lit cigarette, at about 400C will not.
And I've found statements by fire fighters that they have tried to do so, and found that the only way was to atomise fuel onto a red-hot turbo.
Liquid fuel never caught fire.  (Reinforces  the point about the high pressure PI pump).

BUT, I found this video:  http://rebrn.com/re/this-is-why-you-turn-the-engine-off-during-fueling-1816962/
That is odd though - the initial ignition looks more like vapour, or spray going up (see above) and the driver's clothes caught fire, as if he had leaked it all over himself.   And there is a spread of fire along a trail to the right,as if there was already a large pool of spilt fuel, which hadn't ignited until something happened at the back of the bike.  All very strange.

John

[oil_on_the_carpet]

Quoted from JohnD

I am NOT arguing that an inertia switch is a bad idea, but can a hot engine ignite spilt petrol?

It's known and been demonstrated that a lit cigarette, at about 400C will not.
And I've found statements by fire fighters that they have tried to do so, and found that the only way was to atomise fuel onto a red-hot turbo.
Liquid fuel never caught fire.  (Reinforces  the point about the high pressure PI pump).

BUT, I found this video:  http://rebrn.com/re/this-is-why-you-turn-the-engine-off-during-fueling-1816962/
That is odd though - the initial ignition looks more like vapour, or spray going up (see above) and the driver's clothes caught fire, as if he had leaked it all over himself.   And there is a spread of fire along a trail to the right,as if there was already a large pool of spilt fuel, which hadn't ignited until something happened at the back of the bike.  All very strange.

John

and there are no electric items under the bonnet that could be sparking and ignite the spelling petrol?
there is a very good reason your race car has to have an easily accessible battery cut off switch.

[Nick Jones]

Quoted from oil_on_the_carpet

and there are no electric items under the bonnet that could be sparking and ignite the spelling petrol?
there is a very good reason your race car has to have an easily accessible battery cut off switch.

Just so.

When it comes to auto-ignition, brake fluid takes a bit of beating......  That definitely catches fire on a hot exhaust manifold whereas petrol just fizzes.

Nick

[TedTaylor]

I personally feel these remarks implying it is unsafe to run a car with a LOW pressure electric fuel pump and not use an inertia switch are irresponsible.  Effectively you are saying that anyone with a car without such a switch should immediately stop using it until one has been fitted - which means tens of thousands of classic cars in use today all round the world!

Luckily 70 years of use of electric low pressure fuel pumps has shown this to be a fallacy and people with older cars can safely continue to run them without the fear that in the event of an accident they are likely to find their car going up in a ball of fire.  I have been driving since 1960 and in that time I have seen cars at the side of the road burnt out on no more than a few occasions ......... and the last one during last year was a modern diesel engined 4x4 parked in a car park!

Yes fires in cars do happen as recent pictures of cars on fire as a result of a multiple pile up on a motorway have shown ...... but then these cars would have been diesel engined or if petrol injection fitted with an inertia switches anyway!  Tragic when they happen and there is a loss of life or serious injury, but with a low pressure electric fuel pump the incidence is almost unheard of and rarely happens as a result of a crash where the fuel line is ruptured and fuel is pumped out

The reason for the almost non existence of fire in older cars after a crash is what so many people will inevitably have experienced with fuel leaking at low pressure - it DOES NOT form a petrol mist, but drips as a liquid.  To catch fire these drips must first vapourise, and then must achieve a temperature about the flash point of the fuel by being exposed to a source of extremely high temperature, which is what a spark is, or a very hot exhaust.  All points to which John has correctly alluded.

When we have carburettors placed above hot exhausts and leaks happen how often have there been petrol fires?  

To reiterate what John said.  I am NOT saying that inertia switches should not be fitted to LOW pressure electric pump fuel systems but that practice has proven them not to be essential unlike medium and high pressure fuel systems where they are.  

In instances where competition regulations require an inertia switch to be fitted to a fuel system - I have not been involved with competition regulations for 15 years and so do not know what the Blue Book says on the matter but will be seeing a top MSA Historic Rally Scrutineer in the next week or so and will find out for my own interest - but if the MSA require them on a low pressure system it is more related to 'Duty of care' for people competing under their regulations as to the likelihood of a fire incident.  This does not apply in road use.

MUT

[Andy Flexney]

I think the inertia switch might be necessary on a high pressure system but not on one running at 2 or 3 PSI. Cars have been using low pressure electric petrol pumps for over 70 years and most that I have seen do not have an inertia switch.

AndyF

[JohnD]

My comments on the ignition of spilt fuel were purely academic and enquiring.     Clearly  in a crash , sparks or even bdrake fluid could ignite fuel.  And it's your car, your choice, like all safety measures.

For Ted, AFAIK the competition regs speak not of fuel pump cut offs.   Only the FIA. Type electrical one.   But check that it works!   I was at a rally recently when a car had an engine fire.    They pulled the cut off and the exti guisher but the fire kept burning because the cut off did not stop the radiator fan!!!!

Eventually a brave marshal opened the bonnet (they shouldn't do tat) And ripped off the fan wires.

John

[Jonny-Jimbo]

Ignoring all of the above (for I will not comment further on the rights and wrongs of fitting a switch), I am going to fit one anyway.

I had not thought of running one through a relay actually. I think I have a four pin relay somewhere, if not, I'll grab one at the local breakers yard when I go to look for a switch. They occasionally have classics in there too, so if I see anything of interest I'll post about it.

The issue will be seeing what cars they have in and then locating the inertia switch on the car!

[Stuart Wilson]

Quoted from JohnD

   I was at a rally recently when a car had an engine fire.    They pulled the cut off and the exti guisher but the fire kept burning because the cut off did not stop the radiator fan!!!!
John

The fire not going out could more probably be down to the extinguisher, it's well known in rallying that the AFFF extinguishers are no where near as good as the halon/BCF that was used before it was banned. When I built my last rally car I used an inert gas system, I wanted a system that had more chance of working. They say in a competition car the extinguisher is to supress the fire long enough so the occupants can get out

[uksnatcher]

I put a Mondeo mk2/Focus mk1 cut off switch in mine, £5 INC connector (must get connector with some wiring tails, tiny terminals on switch) from ebay

You will find it in the N/S footwell behind the lower side panel or by the fuse board on the Ford if you choose that option, the later models have them just look a bit different with a rubber boot over the button.
Same one is fitted to the JAGUAR S TYPE too
http://www.ebay.co.uk/itm/JAGU.....3:g:YWYAAOxyXDhSdB90



Strange little thing, its a ball bearing and a magnet under the red switch, very clever.



Wired it in by my leg attached to the center frame, never had it trip accidently yet.

[TedTaylor]

Quoted from Jonny-Jimbo

Ignoring all of the above (for I will not comment further on the rights and wrongs of fitting a switch), I am going to fit one anyway.

And I can see nothing wrong with this - perfectly reasonable if I don't sound too pompous in saying so..  My remarks were primarily directed at the comments which implied that all cars with ANY electrical petrol pump should have an inertia switch fitted as they were dangerous without one ....... which would mean all Minis for example, MGs including pre-war models, Morris Minors etc. .......

As I said, when I get my Mk1 PI back on the road, even though it never had one fitted originally I will be fitting one in an inconspicuous place.

MUT

[Jonny-Jimbo]

Sure Ted, all I meant was I could see what everyone meant, I was just saying that I can see there is LESS need for a low pressure pump, but I'm going to fit one anyway, just in case, particularly as I hope to do a few track days in the Vitesse this year. And obviously then it's good to have a cut out.

The main issue I'm having is deciding where to mount the pump - there are fittings in the boot from when the car had KD's race engine in, but also, if I mount it on the block in the pumps original position I don't have to re-do the plumbing. Just a matter of taste really on that front.

[JohnD]

Quoted from Stuart Wilson

The fire not going out could more probably be down to the extinguisher, it's well known in rallying that the AFFF extinguishers are no where near as good as the halon/BCF that was used before it was banned. When I built my last rally car I used an inert gas system, I wanted a system that had more chance of working. They say in a competition car the extinguisher is to supress the fire long enough so the occupants can get out

I think you need to back up that provocative statement with evidence, or risk the wrath of the MSA, for which AFFF or Zero 2000 are the only types of extinguisher allowed.
How long ago did you build your last rally car?   Halon has been banned since 1989, nearly 30 years.  Certainly, the MSA Scrutineers today will not approve an "inert-gas" extinguisher system.  The only type of inert gas system in use at present is CO2, recommended by the Fire Service for electrical fires only, and useless in an car fire as all the CO2 will fall out of the engine bay.    A passenger compartment full of CO2 is not one you would live long in.

John

[Stuart Wilson]

This is the system I fitted to my car which was logbooked in 2007 and used up until I sold in October 2015. No issue with the FIA approved gas system

http://www.f-e-v.co.uk/gas-extinguishers/

Lifeline also do a gas system, ZERO 360
http://www.lifeline-fire.co.uk/motorsport/products.asp?page=zero-360-series-fia-24

[TedTaylor]

Quoted from Jonny-Jimbo

The main issue I'm having is deciding where to mount the pump - there are fittings in the boot from when the car had KD's race engine in, but also, if I mount it on the block in the pumps original position I don't have to re-do the plumbing. Just a matter of taste really on that front.

Could I suggest location in the boot?  Under the bonnet, especially attached to the engine block, brings possible problems of heat affecting the pump.  In the boot you can tap into the feed from the tank to the engine compartment the only extra problem being a good power feed from the front unless the battery has been relocated in the boot.

MUT

[JohnD]

Thank you Stuart!

When the MSA Blue Book says, quote K.3.1.6 "Permitted Extinguishants.  AFFF, Zero 2000" I'm surprised that there is a separate list of FIA approved agents - perhaps not, the MSA is always behind.

Is there nothing but a gas in this system?  What stops it falling out of the engine bay?  Does it carry another material with it?
John