Gordon Smith SV#5 1/4” bore safety valve

[simon822]

Having 2 engines with Gordon Smith safety valves when a friend was having issues with very high hysteresis I offered to make a set for him. To fit into the space available 1/4” bore valves to the SV#5 design dated 24/6/2003 have been manufactured with springs and balls purchased from Polly. Sadly on the first test I was very disappointed by the performance, they were anything but mild, and had a hysteresis of about 15psi. Having checked the dimensions, the shroud was 385 thou diameter and the distance from the ball to the shroud was 93 thou and 97 thou. Would somebody be able to confirm that the dimensions I am using are correct and the drawing I’m working with is correct?

regards,

simon.

[uuu]

I have a drawing "PSV#5" modified 5/10/2011 from Polly for 1/4" bore, showing the diameter of the shroud as 0.385", same as you. The ball projection from the shroud shows as 0.093" to 0.100".

Wilf

[simon822]

Thank you for this. Just what I wanted to hear. I have made a change to the body dimension this evening, the bore was not 15/32, it was 29/64 on one and slightly less on the other, so I have increased the bore to 15/32 on both valves.

Time to try them again.

Regards,

Simon.

[simon822]

Ok, so for an update, the valves worked far better today, lifting fully at about 82 and sitting back by 78. But there is some mild ‘farting’ from the valve when fully open. It’s not a major issue, but would be nice if I knew the reason.

1. The spring is rated at 100psi, but currently set for 80psi.
2. The diameter of the shroud is now 380 rather than the 385 on the recent drawings (my drawings have 380), so less lift
3. The length of the internal adjustment thread is 1/2” rather than 3/8” on the drawing, increased disturbance within the body
4. The ball protrudes 93 thou (I think, the other one is 97 thou but they both have a mild fart.

Regards,

Simon.

[Jim]

Is this drawing of any help?

Jim

[simon822]

Thanks, It is very interesting, I have the drawing for the 5/32” @ 100 psi, and it has a spring rate of 15 lb/in all the other dimensions are the same. You drawing is for 90psi and a spring rate of 13.5 lb/in.

I’m going to see if the owners of the engine are happy with the valves. If they were mine I would look at making changes, but there are other things to be done on the engine as well.

One thing I am planning on doing is raising the pressure from 80 to either 85 as per drawing or 90 as per half the hydraulic test depending upon what out boiler inspectors say.

Regards,

Simon.