Hi Mike,

Thanks for the prompt reply and your offer to design the spring for me.

The valves ( I intend to use two) will have a 3/16" ball and a 9/64" seat as per Martin Evans design in his book 'The Model Steam Locomotive' page 157. I intend to use a soft opening as a Pop action could result in one being burnt when a valve releases suddenly, but I am open to your sugestions.

I will need to know the: Free spring length.

Number of coils i.e. pitch.

Diameter of the mandrel allowing for spring-back.

Wire gauge in mm and the type of wire

.( I have 0.71, & 0.80mm in stainless, and 0.77 & 0.85mm in piano wire and 0.82, 0.91, & 01.0mm in steel wire.

Hope this helps and thanks Mike, Kind regards, Gary Lodge.

Hi Mike,

The seat is flat.

The push rod can be between 3/32" and 1/8" in diameter.

Spring length, I will make valve to suit say between 1/2" and 5/8" long and say 6 to 8 coils.

The diameter of the steam way i.e. the inside dia of the tube above the seat is 29/64" so there is plenty of space for the steam to exit, much more than the 1.1 times the seat area which is I beleive the minimum.

Kind regards, Gary.