Data Sheet

Bulletin 71.4:66
D100152X012
November 2009

TYPE 66R RELIEF VALVE
TYPE 66RR RELIEF VALVE
W1953
W1908

Figure 1. Typical Constructions

Types 66R and 66RR low-pressure throttling relief
valves
(1)
are used to help protect a system against
overpressure, or to maintain an inlet or backpressure.
The standard Type 66R direct-operated construction
is used for 2-inches w.c. to 2 psig (5 mbar to 0,14 bar)
set pressure ranges, while the standard Type 66RR
pilot-operated construction with Type Y695RR pilot is
used for 4-inches w.c. to 4.5 psig (10 mbar to 0,31 bar)
set pressure ranges. However, higher set pressure
ranges are available with optional springs, diaphragm
plates, and other internal parts.
Standard Type 66R relief valves have internal
registration through a stem guide (Figure 2) that
reduces the need for control line piping, while cast iron
body Type 66R relief valves additionally are available
with a sealing diaphragm and a tapped connection
boss on the diaphragm case for external registration
that requires a separate control line. All Type 66RR
relief valves come standard with internal registration in
the main valve body and tapped connection bosses on
the pilot casings for external registration that requires
a separate control line.

  
  —Retainer (Figure 2) in standard
valve plug assembly closes against seat ring
before assembly can overtravel and thus
overcompress O-ring.
  —Steel bodies are
available for increased resistance to piping
stresses or whenever dictated by local codes.
External registration is optional with all cast iron
bodies for wherever a remote control line is
required. These relief valves can be used for
vacuum service in both standard and special
versions, since vacuum service capacity is
comparable with relief service capacity.
  —Fluorocarbon (FKM)
soft parts and stainless steel metal trim parts are
available for high-temperatures and/or special
gases. Optional all-metal seats lessen O-ring seat
erosion problems with coke gas or other corrosive
applications and have knife-edged guides on their
valve plug skirts to help prevent particle
accumulation with dirty service.
1. Throttling relief valve dened in ANSI standard B95.1-1972. Not all codes or regulations permit these valves to be used as nal overpressure protection devices.