Abstract: A reverse buckling disc arrangement for direct mounting eliminates separate inlet and outlet seating rings for the disc flange. Centering ring units on both sides of the disc have flanges doubling as the seating rings. The centering ring projecting toward the higher pressure supports a screen for protecting the disc dome while permitting necessary flow-through.

Abstract: An adjustable drop nipple is disclosed for installing fire protection sprinkler systems which comprise sprinkler head assemblies of the dry, pendant type. The downwardly extending length of a drop nipple having a sprinkler head thereon is adjusted by sliding the nipple axially in a collet having an externally tapered section that engages an internally tapered section of a stationary collet holder. When a selected drop length has been established, the collet is then compressed axially against the collet holder with tightening means whereby the nipple is firmly gripped by the collet so that axial sliding thereof is prevented, thereby maintaining the nipple at the selected drop length.