Precision - Type 77 Vacuum
  Bellofram's Type 77 Vacuum Regulator incorporates a fixed negative 15 psig bias spring to maintain vacuum outputs up to 29" Hg. An adjustable opposing range spring increases controlled pressure outputsup to 150 psig. Output pressure droop under varying downstream flow conditions is minimized by use of an aspirator tube which adjusts the air supply valve opening in accordance with flow velocity. A balanced supply valve, utilizing a reinforced rolling diaphragm, keeps regulator output virtually immune to changes in supply pressure. Stack-up construction makes the Type 77 easily serviceable, without removing it from the air line.

Applications
The Type 77 provides precise control in subatmospheric pressure applications. specific uses include sample collecting systems, air quality monitoring, parts coating operations, and other industrial functions requiring controlled system pressure from 29" Hg vacuum to 150 psig.

Features
• Single-unit control of pressures from 29" Hg vacuum to 150 psi.
• Flow capacity up to 40 SCFM.
• Dampening action of aspirator tube maintains stable output pressure.
• Output virtually unaffected by changes in supply pressure.
• Can be disassembled and service without removing from line.

Operation
The regulator may be installed either upstream or downstream from the vacuum pump. Upstream installation is preferred when rapid evacuation of a vessel or system is required, because the exhaust capacity of the pump is normally greater than that of the regulator. In all other applications, the regulator can be located between the pump and the vessel. When the adjustment knob is turned to create an output setpoint, the range spring exerts a downward force on the signal diaphragm, which causes the supply valve to open. Output pressure, combined with the negative bias spring, creates an upward force on the diaphragm assembly. When the setpoint is reached, the two forces are in balance. If output pressure exceeds the setpoint, the excess pressure is transmitted through the aspirator tube to the bottom of the control diaphragm. This moves the diaphragm assembly upward, closing the supply valve. Excess output pressure is vented until the setpoint is again reached.