GX CS-4....... Lost check valve ball

Hello members

I have managed to lose the ball that is in the check valve of the CS-4
So, when the chuckling stops, I'd like to know the diameter & material in order to find a replacement, please.
Any help. including links appreciated

EDIT
The ball in question is the one that is part of the Burst Disc assembly
(Next to the greas pot)

Thanks
Edward
 
Last edited:
This one...?
GX pumps have this as a unit, but 'out of stock' at the moment.

Check valve.jpg