Sorry for the poor images. I don't have a high quality camera. This is the lift valve off one of my Q series Bolens. They used the same one for the QT-16 and QT-17. It also appears to be the same valve used on other models.
Once the spool is removed you can see what looks like an O ring at each end.
They aren't. They're more like tiny versions of the bearing seal you would use on an axle shaft.
One side of the ring is solid and the other is U or C shaped. I don't know what they are called, but read "Lip Seal" on a post. The size is approximately 1/2" OD x 5/16" ID x 1/8" thick. Anyone know of a source for these? Bolens offered a rebuild kit, but a google search came up blank. Thank you, Paul.