Hi, Im new to the boards. I am currently designing a spool valve for a paintball gun. The operating pressure will be around 100-250psi. The type of orings I will be using will be polyurethane. They will be lubricated using  DOW 33.

My problem is I am not sure of the size of orings I should be using. The interior of the sleeve is .7", the spools are currently .25" in length. The spools will have to be smaller in the finished produc. Can anyone with some expieience please recommend and oring size and if possible give me the dimmensions for the slot needed (I have some refrence books but they are not availible to me for several weeks).

If you need more specifications to solve my problem please post them up.