I have some Tyler systems that are in need of filter/dryer changes. The problem is the piping is arranged like this:

king valve>dryer>sight glass>service valve>solinoid valve.

The problem is that once I close both valves to isolate the filter, I have no access to the system. If I use the service valve for access, I will be pulling a vacuum backwards against the solinoid valve. will a solinod valve prevent reverse flow? I wouldn't think so, but maybe I'm wrong.