Inlet non return valve.

[vincereynard]

No 1 inlet is connected to the vaccum tank through a non return valve, the brake servo off
cylinder 4 does not have one.

Any reason for this?

[tonyr27]

The servo unlike the vacuum switch when closed is not open to the atmosphere.

Had fun driving on the motorway with a broken non return valve.

TonyR

[Grizzly]

Brake servo has a one way valve built in.

[vincereynard]

Thanks! I just wondered.

[elanman999]

Early +2's had a NRV in the pipe to the servo, it was attached to the bulkhead and rattles when running slowly. Not sure if the later cars had one.

Cheers
John

[CBUEB1771]

Hmm, the Service Parts Lists for both the Elan and the +2 suggestive the non-return valve, 050 J 6019 was fitted to all with brake servos. It is not fitted to the cylinder head, as stated in another reply, it is fitted to the section of Bundy tube that leads to the servo(s). The non-return valve is threaded on one end for the Bundy tube and has a hose barb on the other end for the flex line that goes to the barbed fitting screwed into cylinder #4 inlet port.

[vincereynard]

So it may have been present but it should not be necessary? I could use the one off the headlamp system. Toad has electric lift so it is no longer used. (Even though all the pipework is (was) still there.)

Is there any point?

[draenog]

Brake servo has a one way valve built in.

Depends on the servo. If the plastic connector on the servo is white it's a non-return valve. If it's red it's simply a slave adaptor. See this link:

http://volvo1800pictures.com/document/Girling%20Hydralic%20Servo%20unit%20MK%202A%20and%202B/Girling%20Hydralic%20Servo%20unit%20MK%202A%20and%202B.pdf

My +2 has a red slave adaptor in the servo and a NRV in the pipe. The NRV and pipe are similar to this:

http://www.ebay.co.uk/itm/Mk2-Lotus-Cortina-Series-2-Mk2B-Girling-Remote-Servo-Vacume-Pipe/181409821171?hash=item2a3cde31f3:g:y5MAAOxyyFhTc1Ig

[CBUEB1771]

My +2 has a red slave adaptor in the servo and a NRV in the pipe.

Very interesting, my mid-1971 build Federal +2S has the red plastic hose connection on the servo and the NRV in the line to the cylinder head.

[Grizzly]

Brake servo has a one way valve built in.

Depends on the servo. If the plastic connector on the servo is white it's a non-return valve. If it's red it's simply a slave adaptor. See this link:

http://volvo1800pictures.com/document/Girling%20Hydralic%20Servo%20unit%20MK%202A%20and%202B/Girling%20Hydralic%20Servo%20unit%20MK%202A%20and%202B.pdf

My +2 has a red slave adaptor in the servo and a NRV in the pipe. The NRV and pipe are similar to this:

http://www.ebay.co.uk/itm/Mk2-Lotus-Cortina-Series-2-Mk2B-Girling-Remote-Servo-Vacume-Pipe/181409821171?hash=item2a3cde31f3:g:y5MAAOxyyFhTc1Ig

Ahh ok, didn't know there was two different versions...... I'm fairly sure my +2 doesn't have a non return valve in the metal pipe but it has a white valve (the same as my 2 seater) which would explain why.

[CBUEB1771]

Is there any point?

Yes, there is a point, the non-return valve prevents fuel-air mixture from being drawn into the servo. The non-return valve servo also has a larger bore, and perhaps a lower cracking pressure than the one used for the headlamp vacuum system. Using the headlamp non-return valve in the servo circuit could possible slow the response of the brake servo.

[vincereynard]

By - "is there a point" I mean considering it does not have one at the moment.

Therefore, presumably, it already has one in the Servo. Which is a later Lockheed unit.

As it works, I assume there is no point putting another NRV into the pipe.

[nmauduit]

, and perhaps a lower cracking pressure than the one used for the headlamp vacuum system. Using the headlamp non-return valve in the servo circuit could possible slow the response of the brake servo.

if the servo is not seriously leaking vacuum (which would mean it needs overhaul) I would not worry about response variation due to vacuum intake restriction : it operates on the vacuum level accumulated within its toroidal housing, and does not normally require significant pulling of vacuum continuously.

[vxah]

is got me thinking, how much would the vacuum signal be changed with a check valve at the servo end of the pipe compared to the valve at the manifold runner? In an ordinary set up where the plenum has all cylinders connected it's not an issue but, the piston going down the bore creates a low pressure, this is transferred to the port runner because the inlet valve is open, the low pressure is created because the throttle flap is almost closed.. The volume of the port and the amount of air flow past the throttle flap must determine the peak depression and how quickly it decays, the same on all four cylinders? Except for No4 which has an increased port volume due to the length of servo hose? Could the peak depression be less with a longer decay time?
If the check valve was on the runner there would be no change port volume once the servo hose has matched the peak depression?
Shall I get my coat?