A vacuum system pipe coupling includes a first coupling member and a second coupling member. The vacuum system pipe coupling has a seal system that is to be positioned to seal between the first and second coupling members and a securing system to releasably secure the first coupling member to the second coupling member. The seal system has an inner seal element and an outer seal element spaced from the inner seal element. The first coupling member is provided with a flow passage configured to conduct a pressurized gas to a space between the inner and outer seal elements to shield the outer seal element from fluid flowing through the pipe coupling in the event of failure of the inner seal element.