Lotus Elan

Headlamp lifting mechanisum - Vacuum tank

PostPost by: terryp » Mon Jun 03, 2019 7:37 am

Hello all
I know I havent been here for a while but now I have sold my Elan :( (So 12 years of Elan ownership comes to an end)
I now have 2 x Ginetta G4 , one is a later S4 type and I have found an original pop up headlight bonnet. These bonnets were replaced as they couldn't get the reliability using a motor.
My question is , if I rig up a failsafe type arrangement with a Vacuum pod similar to the later Elans, do you still need a vacuum reservoir? i.e was the reservoir used for when the headlights were being lifted rather than pulled down?
Thanks
Terry
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PostPost by: nmauduit » Mon Jun 03, 2019 12:47 pm

I would think the vacuum reservoir has the purpose of granting immediate and fast action at all times. If you're happy with waiting that you have enough vacuum at the manifold (depending on your engine cam profile, and rpm) to raise you headlights you should be able to operate without vacuum tank. You can always stick an aluminium bottle later on the pod side of the vacuum one way valve if you change your mind.
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PostPost by: terryp » Mon Jun 03, 2019 1:00 pm

Thanks but with the failsafe design , you pull the headlights down, does that mean they will slip up under load?
Thanks
Terry
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PostPost by: pharriso » Mon Jun 03, 2019 2:51 pm

terryp wrote:Thanks but with the failsafe design , you pull the headlights down, does that mean they will slip up under load?
Thanks
Terry


Not if you have a non-return valve in the line.
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PostPost by: terryp » Mon Jun 03, 2019 2:52 pm

So Phil, what was the reason for the tank on the failsafe design?

BTW hope you are well

Terry
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PostPost by: steve lyle » Mon Jun 03, 2019 2:54 pm

Yes, the later models with the fail-safe system still used the cross-member vacuum tank.
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PostPost by: john.p.clegg » Mon Jun 03, 2019 4:04 pm

Larger throttle opening produces little vacuum, with the failsafe headlights,your headlights will start to rise ,with the earlier system they will start to droop ( without a larger vacuum resevoir )..

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PostPost by: vxah » Mon Jun 03, 2019 4:28 pm

Plus of course you need a reasonable vacuum reserve to keep the lights down when parked. I guess even the rubber hoses etc will seep air through given time? I like them to stay down for at least a couple of days..
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PostPost by: terryp » Mon Jun 03, 2019 5:23 pm

So I will need a little tank somewhere. Perhaps a modified alloy catch tank or something.
Thanks everyone, now to find the parts!
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PostPost by: RichardHawkins » Mon Jun 03, 2019 7:26 pm

Terry,

Vacuum tank design is a little tricky. Cylindrical or spherical is best. If the vessel is under pressure, the medium within the vessel will hold the vessel in shape, like a beer can, but apply avacuum and the beer can will collapse. I am not able to give specific design advice, but he general principle applies.

Hop this helps,

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PostPost by: nmauduit » Mon Jun 03, 2019 8:50 pm

pharriso wrote:
terryp wrote:Thanks but with the failsafe design , you pull the headlights down, does that mean they will slip up under load?
Thanks
Terry


Not if you have a non-return valve in the line.


and no leak... but that's possible with a clean and well maintained vacuum circuit.

The vacuum tank is an other issue, if you feel like saving weight it should be possible to operate without, esp. a failsafe version... Then if you change your mind, you can always make one out of an alloy drinking bottle (like for going camping).
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PostPost by: terryp » Fri Jun 07, 2019 8:34 am

Nice idea about the flask :-)

I will get the mechanium working and then try to obtain a cheap vacuum unit.
Thanks

Terry
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PostPost by: pharriso » Fri Jun 07, 2019 11:50 am

terryp wrote:So Phil, what was the reason for the tank on the failsafe design?

BTW hope you are well

Terry


I guess it was already there! On my car one of the DPOs designed out the vacuum reservoir & dash mounted vacuum switch & fitted an electrical vacuum solenoid near the headlights (a la late Plus2). Works perfectly!

Life is good thx. Sorry to hear you've sold the elan!
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PostPost by: terryp » Fri Jun 07, 2019 12:08 pm

Phil
Yes I think you are right, I don't think the tank is required for a failsafe design. The only issue would be having enough vacuum to pull the lights down (after having them on) and if you were on full throttle (!) it may take a little longer. I think I will risk it!
Thanks
Terry
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