The design doesn’t call for such a need.
The sight glass itself would prove to be a potential leak down the road with susceptibility to pressure.
The schraeder valve does the same as a sight gauge, it detects how much air is against the bladder; water through this valve indicates that the bladder has ruptured.
I doubt if they ever will make such a gauge, the design of the product now provides good reliability.
I know this from a residential point of view, not commercial.
» This message has been edited by DUNBAR on 08 March 2004