Vacuum spigot for airhorn pump

This converts a small airhorn pump to supply vacuum brakes on a miniature train. These are typically 5" or 7 1/4" gauge in most places, or 4 3/4" or 7 1/2" in the USA

Glue the spigot over the inlet hole as shown. We used Loolifl because it is flexible and dries quickly.

With the common pumps as shown you should not need to change any dimensions but if you encounter a different shape then the SCAD file might help.

Warnings.

Take care when ordering the pump. Temu advertise several pumps as "12/24V" without allowing choice at purchase time. Then they ship the 12V version. For a car horn that only sounds briefly this might not matter, but a train driver must always be able to run the brake pump for as long as needed to operate all the brake cylinders on the train. So use a 12V pump on a 12V system and a 24V pump on a 24V or 20V system.

Many pushbuttons cannot handle a large DC current so use an automotive horn relay between the button and the pump.

To avoid breakage of the spigot we suggest using a very short length of soft transparent tube to connect the spigot to a typical hard plastic vacuum line.

As always in miniature passenger train operation, test the brakes before each steep descent so that in the event of train pipe or pump failure you can stop before a brake failure matters.