Lotus Elan

Fuel cut Inertia Switch.

PostPost by: Grizzly » Sat May 19, 2018 1:42 pm

I've just been reading a post on a Mini Forum about some thing similar, a guy had wired up his electric pump through a Oil pressure switch but the problem was his car only makes 15psi at 900rpm and the switch triggered at 8psi, so he was cranking at 250rpm and only just getting enough oil pressure when his battery was 100% (pig to start cold), so he's been told to fit a bypass from the starter to start the pump.


Interesting.......


Aren't the fuel filler caps vented on a 2 seater Elan?
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PostPost by: billwill » Sat May 19, 2018 1:56 pm

Grizzly wrote:The crazy thing is i'm starting to have second thoughts about the electric pump, without any safety back up i do like how it starts from cold but apart from that it starts just the same day to day as the mechanical pump...... But if i fit a Oil switch to the Electric pump then i loose the advantage of being able to Prime the carbs before i start cranking, then there is the Inertia Switch which seems a bit of a unknown quantity? Will it cut out in a low speed collision? Do i need a sensitive Inertia Switch for a GRP car (as people are telling me) or do i need a less sensitive switch as it's a sports car?


In lotus-carbs-f40/electric-fuel-pump-noisy-idle-t20354-15.html#p117904 I showed a circuit which could use lack of oil pressure to stop the electric pump. This does of course mean that you need a priming button to start the car. This should be a hold-down button not a switch, so that you wont forget to release it when the engine is running.



Image


You could of course also add an inertia switch to such an arrangement.
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PostPost by: Bud English » Sat May 19, 2018 3:00 pm

Way back when, I had a '70 Vega that had a timed relay in the oil pressure cutoff circuit. It activated during cranking, bypassing the oil cut out switch for about ten seconds, and then turning off. I found out about it by accidentally knocking the connection off of the oil pressure switch when changing the oil filter. The car would run for ten seconds then die. PITA to troubleshoot when you didn't know know it was there.

But then, at what point do you stop adding "what if" relays?
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PostPost by: Bigbaldybloke » Sat May 19, 2018 6:12 pm

I?ve just fitted an electric pump and inertia switch. The switch is a ford one and I have mounted it upright on the bulkhead under the bonnet near the starter solenoid and bonnet catch. I made a simple aluminium mounting bracket for it as the bulkhead is not vertical there. The switch has a changeover contact so you use the one that is normally closed when the switch has not tripped to power the pump and you could run a wire from the normally open contact to operate a warning lamp in the car to show if the switch had tripped. I haven?t done this but might do if I get time.
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PostPost by: AussieJohn » Sat May 19, 2018 7:12 pm

My tvr griffith was damaged when I bought it and the inertia had tripped, it was mounted behind the glovebox onto grp.
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PostPost by: RichardHawkins » Sat May 19, 2018 8:48 pm

An inertia switch from a Lotus Elise might be the one to use.

The only time mine operated was when I slipped with a srew driver whilst changing the air filter. Unfortunately I don't remember exactly how the switch was attached to the vehicle other than that it was close to the air filter.

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PostPost by: Peter +2 » Sun May 20, 2018 8:31 am

This is the electrical type, i used, "MK1 GOLF CABRIO Fuel Pump Relay, With Fuse - 321906059C?

https://www.ebay.co.uk/itm/MK1-GOLF-CAB ... 5b39a1f0e6

I understood it had a built in timer to allow the pump to prime, but either the prime time is to short or I am wiring it up wrong, possibly the latter. (I am using a Huco pump)

In hindsight the Inertia type seem to be the better choice and something which I will now consider and I will be following the conclusion of this thread.

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PostPost by: Andy8421 » Sun May 20, 2018 11:44 am

billwill wrote:
Grizzly wrote:The crazy thing is i'm starting to have second thoughts about the electric pump, without any safety back up i do like how it starts from cold but apart from that it starts just the same day to day as the mechanical pump...... But if i fit a Oil switch to the Electric pump then i loose the advantage of being able to Prime the carbs before i start cranking, then there is the Inertia Switch which seems a bit of a unknown quantity? Will it cut out in a low speed collision? Do i need a sensitive Inertia Switch for a GRP car (as people are telling me) or do i need a less sensitive switch as it's a sports car?


In lotus-carbs-f40/electric-fuel-pump-noisy-idle-t20354-15.html#p117904 I showed a circuit which could use lack of oil pressure to stop the electric pump. This does of course mean that you need a priming button to start the car. This should be a hold-down button not a switch, so that you wont forget to release it when the engine is running.



Image


You could of course also add an inertia switch to such an arrangement.


While this circuit will work, it doesn't follow good safety practice in that it won't 'fail safe' as it requires the wiring and oil switch all to be intact and work following an accident to switch off the pump.

Demon Tweeks sell an oil pressure switch with changeover contacts, so you don't need the relay - and it will fail safe. I have this and a priming pushbutton on the Elan I race(d). I have it wired so it cuts the ignition circuit as well, which has the added advantage of killing the engine if you lose oil pressure for non accident related problems.
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PostPost by: Bud English » Sun May 20, 2018 2:14 pm

Andy8421 wrote:While this circuit will work, it doesn't follow good safety practice in that it won't 'fail safe' as it requires the wiring and oil switch all to be intact and work following an accident to switch off the pump.


You'll have to explain how that works. As I see it, if any of the circuit (battery, oil switch, relay, wiring) isn't intact, accident or not, the pump won't run. The relay doesn't latch. It's not a matter of "switching off" the pump.

This circuit was suggested to use in addition to the fuel cutoff impact switch and isn't, by itself, intended to shut off the fuel in case of an accident.
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PostPost by: billwill » Sun May 20, 2018 9:57 pm

Bud is right, the circuit is not fail-safe, so if one can get hold of a oil pressure switch with changeover contacts that would be better and the circuit much simpler. .
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PostPost by: Andy8421 » Mon May 21, 2018 3:17 am

Bud English wrote:
Andy8421 wrote:While this circuit will work, it doesn't follow good safety practice in that it won't 'fail safe' as it requires the wiring and oil switch all to be intact and work following an accident to switch off the pump.


You'll have to explain how that works. As I see it, if any of the circuit (battery, oil switch, relay, wiring) isn't intact, accident or not, the pump won't run. The relay doesn't latch. It's not a matter of "switching off" the pump.

This circuit was suggested to use in addition to the fuel cutoff impact switch and isn't, by itself, intended to shut off the fuel in case of an accident.


Using the circuit above, for the pump to switch off, the relay has to be energised. For that to happen, the oil switch, the relay, the wiring to the oil switch and associated power supply wiring needs to be intact - which may or may not be the case in an accident. Using a changeover switch eliminates this vulnerability. Rip the wires off the switch and the pump will stop.

Clearly if the wiring to the battery or the pump is damaged, then the pump will stop anyway.

Demon Tweeks don't seem to sell the switch anymore, but this seems a good substitute, and has the benefit of being adjustable:

http://www.oem.co.uk/products/Pressure_ ... 09326.html
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PostPost by: Bud English » Mon May 21, 2018 6:36 am

You are totally correct Andy. I was looking at the operation of the relay circuit completely back-asswards. :oops:
The oil FAIL light should have been my first clue.
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PostPost by: billwill » Mon May 21, 2018 11:28 pm

Andy8421 wrote:
Clearly if the wiring to the battery or the pump is damaged, then the pump will stop anyway.

Demon Tweeks don't seem to sell the switch anymore, but this seems a good substitute, and has the benefit of being adjustable:

http://www.oem.co.uk/products/Pressure_ ... 09326.html


Ah, it seems they are not actually adjustable, you just buy the one with the range that you desire.
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PostPost by: Andy8421 » Tue May 22, 2018 3:26 am

billwill wrote:
Andy8421 wrote:
Clearly if the wiring to the battery or the pump is damaged, then the pump will stop anyway.

Demon Tweeks don't seem to sell the switch anymore, but this seems a good substitute, and has the benefit of being adjustable:

http://www.oem.co.uk/products/Pressure_ ... 09326.html


Ah, it seems they are not actually adjustable, you just buy the one with the range that you desire.


Bill,

If you download the PDF on the page I linked to it shows the adjustment range of the different variants. The most likely candidate for our use would be:

Part number 0170457041318, Adjustment range 0.3-1.5Bar, Fitting 1/8"NPT

I am sufficiently pleased with myself for having found this, I am going try to order a couple as spares.

Andy.
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PostPost by: rgh0 » Tue May 22, 2018 1:06 pm

If you have a Plus 2 you really need more than just a pump cut off as the tank is above the carbs and will flow under gravity if damage occurs in the fuel lines or carbs. My S1 Esprit has a inertia cut of switch for the electric pump plus a cut off valve in the fuel line from the tanks as the top of the tanks is above the carbs like in the plus 2.

cheers
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