In the quest to make the M91 do some work, I took a day off from building the woodworking shop, to experiment with check valves for a wooden body, brass sleeved piston and block water pump idea I have cooking.
I needed check valves. A rather long google session last night brought no results I was happy with. The concept is a high bypass, therefore low back pressure, check valve for a tiny water pump.
So if it’s not readily available, or at least I can’t find anything suitable (no plastic, if you please), it was time to make them.
I built a prototype, then reworked it to minimize overall length. The result is the inlet side valve that will be glued straight into the maple cylinder head. Tomorrow I plan on making the outlet side version.
The nitty gritty is as follows:
I mined the telescoping brass tube I have, and began with a tube that is 3/16 OD as the “inner” tube, inlet and outlet. That gave me .160” or so ID. That was perfect for a copper plated common steel BB as a valve ball.
The trick was getting enough bypass to limit back pressure when in “flow” mode.
So to do that, the middle layer, the next size larger tube, was cut to length, and the middle 3/4 or so of it slotted lengthwise, removing roughly half the material, leaving behind a “cage” in the middle section. The outlet end, opposite the tapered seat the ball will drop into when reverse flow occurs, I cut slots in as well, leaving only the very furthest portion intact. That whole. business slips inside an outer 1/4OD tube, which forms the check valve body. The overall dimensions are 1/4 OD, x .830” long. If I were to use it as as an in-line check valve, rather than mounted directly into the block, I’d leave a hose barb on the outlet side as well, making the whole business an inch long. For use pumping water, I used thick CA to assemble the pieces. If and when I build one for the fuel line on the engine, I’ll solder it.
To test it, I attached that spare bit of fuel tubing supplied with the M91 engine, and by simply drawing water from a cup by mouth, it’s very free when in bypass mode, and slams shut dutifully to prevent back flow, regardless of orientation.