Lotus Elan

Servo One Way Valve

PostPost by: William2 » Tue Mar 24, 2015 5:09 pm

I have fitted a new replacement servo to my S4 Elan and in the instructions it says that it has a one way valve fitted in the servo in the vacuum hose input. Does this mean that it is not necessary to fit an additional valve in line with the vacuum hose? If one is required can anyone recommend one that works. There are quite a few on Ebay.
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PostPost by: billwill » Tue Mar 24, 2015 8:26 pm

My opinion is that in those circumstances you could get bye without another one-way valve, but you will get air going in and out of the vent in throat 1 while the air compresses and expands in the long tube to the servo and the front-rib vacuum reservoir, which might disturb the airflow pattern.

So it might be best to fit another one near the carb.

This is all supposition though, the effect mmight be negligible.
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PostPost by: 512BB » Wed Mar 25, 2015 9:26 am

Bill wrote: This is all supposition though, the effect mmight be negligible

You appear to have developed a stutter Bill :lol:

Will,
There should be a non return valve at the manifold take off, but these are sometimes omitted. Then, there is very often a little bulbous NRV in the line about a foot from the manifold. At least there is on my Sprint which MM built, so I am fairly sure it will be original.

I have a spare one of those if you want it, but you will actually have to purchase it outright. I cannot keep hiring you my fings :lol: :lol: Let me know by email if you do.

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PostPost by: billwill » Wed Mar 25, 2015 12:58 pm

PS: When I first wrote my message above I had forgotten about the reservoir, so I think you definitely need a non return valve beteen the manifold and the reservoir otherwise your braking foot pressure will be very dependent on whatever your engine is doing at the time.

The function of the reservoir is to build up a store of 'vacuum' so that the braking is independent of engine activity and it won't be able to do that without an NRV on the monifold pipe.
Bill Williams

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PostPost by: William2 » Wed Mar 25, 2015 6:00 pm

I have attached a photo of the inlet manifold connections thus far. I bought all the parts from Miles and have connected the one way valve for the headlamp vacuum as he suggested using the correct type of hose either side of it. As you can see in the photo the servo take off is right near the manifold and yet to be connected up.
Attachments
Servo 001.JPG and
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PostPost by: Mick6186 » Wed Mar 25, 2015 6:03 pm

The Girling mk2b servo has a one way valve on the input to the servo cylinder and my +2 130/5 has a straight through output from the manifold without a one way valve.
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PostPost by: tfb0001 » Thu Mar 26, 2015 1:45 pm

I use a NRV at the manifold as well, works fine with booster and head lights. BMW # 34331151533 is a good, cheap valve, fits hose diameter perfectly. '69 Elan S4
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