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735 Series LiquiSealTM Purge Control

  • Fully integrated air purge regulator and level transmitter
  • Operation based on the control regulating a continuous 1 cfh (cubic foot per hour) flow of compressed air into the tank downpipe
  • Provides a 1:1 pressure signal to a compatible indicator or external transducer through 1/4 in. airline tubing
  • All LiquiSeal™ purge controls feature an internal isolation diaphragm
  • Back pressure created by the continuous purging of the downpipe is applied to this internal diaphragm
  • Working as a pneumatic transmitter, an equivalent pressure is generated on the gauge side of the diaphragm, which isolates downstream components from contact with the liquid or vapor releases

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SERIES 735  
FITINGS 1918 None, 1/4” NPT 3918 Polyflo; (1) 3/8" tube, (2) 1/4" tube 4918 Swagelok; (1) 3/8" tube, (2) 1/4" tube (
compatible with copper or poly tubing)
PRESSURE OUTPUT 38 25"-650" SafeGard range 48 650"-1750" SafeGard range 58 Without SafeGard option

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Temperature range 0 °F to 120 °F/-16 °C to 54 °C
Maximum pressure 300% over-range
Burst pressure 200 psi
Compressed air requirement 35 psig to 150 psig supply pressure at control inlet. (Minimum supply pressure should be at least 20 psig greater than anticipated maximum liquid head pressure.)
Maximum depth measurement 1,937 inH2O (49.0 m water)
Purge control Unit incorporates differential air flow regulator with flow control orifice
Fixed differential set to nominal 10 psid
Output is 1:1 pneumatic pressure (hydrostatic force equivalent)
Flow rate (air purge) Nominal 1 cfh (cubic feet per hour) at specified differential
Maximum air consumption under 5 cfh.
Materials Machined Brass body with acrylic semi-gloss enamel finish; integral filter element is aluminum with acrylic semi-gloss enamel finish
SafeGard option An adjustable pressure-limiting control that permits pre-setting a maximum value for pressure output from the Purge Control. SafeGard range available as 25 inH2O to 650 inH2O or 650 inH2O to 1750 inH2O

Options & Accessories

Downpipe Check ValveDownpipe Check Valve

6363 Downpipe float check valve, 3/4” NPT connections
6563-10 Downpipe float check valve, 3/4” NPT outlet, 3/8” tube inlet


  • Prevents siphoning or backflow of liquid through a downpipe installed in tank level gauging applications
  • Utilizes a specially designed float pin that rises up to seal the valve shut when liquid enters from the downpipe through the bottom of the unit
  • The advantage of a float check is that it doesn’t create a pressure drop that would affect the level gauge reading (Spring-loaded check valves can impact the accuracy of a downpipe or bubbler system if installed at the tank entry point)

NOTE: Not recommended for use with heavy diesel fuel oil or other high viscosity liquids. Installation in conjunction with a gate valve will permit removal of check valve for inspection and cleaning. (We recommend cleaning the check valve once per year to ensure reliability.)

Material: 304 Stainless Steel, Nylon (float), FKM (seals)
Max. Pressure: 150 psig
Inlet/Outlet: 3/4" NPT-female
Weight: 1.2 lb (0.5 kg) 


Download 6563 Downpipe Check Valve Data Sheet_1200-30

7333-10      Replacement filter element
7334-2        SafeGard service kit
7334-9        Air control section kit
7334-21      Sensor section kit*
7366-1        Orifice/check valve
6448-22      Sensor diaphragm, titanium

* Includes 7366-1 orifice check valve and 6448-22 Titanium diaphragm

A precision pneumatic control valve which will instantly close bubble-tight when subjected to a pre-set pressure.  It is used to prevent overpressuring an indicator.

To order, see Ordering Information chart and Part Number Example above.

1-1/2" NPT Tank Top Fitting (for 3/4” Pipe) single purge line connection with tube fitting
7746-13    Carbon Steel, polyflo 3/8" tube
7746-15    Carbon Steel, Swagelok 3/8" tube
7746-18    316 Stainless Steel, Swagelok 3/8" tube

1-1/2" NPT Tank Top Fitting (for 3/4" Pipe) with single 1/4" NPT purge port connection
2000FA    Carbon Steel
2000PA    PVC    
2000SG    316 Stainless Steel

1-1/2" NPT Tank Top Fitting (for 3/4" Pipe) with two 1/4" NPT purge/equalizer connection
2000FA-2   Carbon Steel
2000PA-2   PVC
2000SG-2  316 Stainless Steel

WARNING: This product can expose you to chemicals including Lead and Nickel, which are known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov