Hi Greg,
You can run the unit without the check valve. Just be sure that no water will enter the orifice (i.e. get it away from water, especially when you rinse the counter lungs, or leave it pressurized).
The rEvo1 I had did not have a check valve afer the orifice and it worked. Even with a clogged orifice it worked ... at 60m!
Maybe it would be wiser to change it. McMaster-Carr should have a replacement part.