I built all of my check boiler valves except for the one on the mighty Falk #1. All of those operated off of the axle pumps and duplex pump (Shay) are of 1/4" OD brass pipe, but those I made for use with the Super Scale Economy injectors are 5/16" pipe and 5/16" check ball. I made sure that the ball could raise high enough to offer absolutely no restriction to flow from the injector. The valve design has worked perfectly so I have seen no reason to change it after 15 years Jesse MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.