MIFAB model MR-500 pressure drop activated brass trap seal primer, with inlet opening of 1/2 in (13) male NPT and outlet opening of female 1/2 in (13) NPT Complete with four view holes and removable filter screen. Serves up to 6 floor drain traps and requires no adjustments and no airpre-charge. A pressure drop of three p.s.i. will activate all of the trap seal primers. MIFAB's Series of trap seal primers can be disassembled in the field. Their unique design permits filter replacement without affecting the performance of the primer. The "O" ring seals are tested for reliability at a temperature range of -40 deg to 450 deg F. The M-500 Series of trap seal primers do not require adjustment. The operating range for all of MIFAB's Series of trap seal primers is 20 to 80 sq psi.