Wright-Austin ST and 31L-ST Gas Liquid Separators
Cast Iron separators with integral drain trap
up to 40% by weight of the units flow capacity

gas liquid separator with trap SIZE CONNECTION PART NUMBER
¾" FNPT 0.75STBN
1" 1.STBN
1¼" 1.25STBN
1½" 1.5STBN
2" 2.STBN
2½" FNPT 2.5STBN
3" 3.STBN
4" 4.STN
5" 5.STN
Performance Overview
ST separators are designed to remove entrained liquid and solids from air, gas or steam.  Their integral drain trap allows fluid to drain from the system without a system pressure drop.  This specific design is effective for applications where the entrained liquid flow rate is up to 40% by weight of the units flow capacity.

The ST is easy to install and has a small footprint compared to installing two separate separator and float drain trap units. Removal of the bottom flange releases the trap mechanism for inspection. All drain trap components are made of rust-proof stainless steel and include a nonmagnetic 18-8 stainless steel valve and seat.  

When properly sized, this separator will remove up to 99% of all liquid and solids greater than 10 microns in size from an air, gas or steam flow.  The removal is accomplished by a design that causes the air/gas/steam to enter a controlled centrifugal flow.  This results in forcing the entrained material to the outer wall and the VCP prevents re-entrainment.

Cast iron ST separators are constructed to ASME code for unfired vessels, Section VIII, Division 1 but NOT stamped. Code stamp and CRN not applicable to this product.

ST Separator Options:

• ½" thermometer connection.

• 50 wt, 120 volt, self-limiting heating element for applications below freezing. The heater does not increase line temperature and can be easily removed for inspection. Add an "H" to the part number after the "ST"; adds 3.5 lbs. to the weight.

• It is typically recommended that for steam service, stainless steel orifices are used on the drain trap instead of the standard viton. Please let us know if this is the case.


If you need assistance with proper selection, please fill-out our inquiry form.

Lead Time:
ST gas/liquid separators usually ship within 7-10 days after receipt of an order.  If the lead time is critical, please contact our office and obtain a lead-time estimate based upon the current manufacturing backlog. 

Type 31 LST gas liquid separator
250 PSI @ 450°F
1" 1.31LSTN
1¼" 1.2531LSTN
1½" 1.531LSTN
2" 2.31LSTN
2½" 2.531LSTN
3" 3.31LSTN
125 PSI @ 450°F
4" 4.31LSTFN
Low Profile Design
The Type 31L-ST is a horizontal, in-line separator is very compact and can be supported by the line in which they are installed, an important consideration in space restricted applications. These units would require a "special order". Expect a lead time of around 12-14 weeks.

Repair kits for the float drain trap assembly for either the ST or LST are P/N 90-0-8C.

• Click on part number for the corresponding drawing
ST Parts List

Air Sizing Chart
Steam Sizing Chart

Formulas and Constants
• Torque spec for body and drain trap bolts are 255 in-lbs.

ST Separator/Trap
31LST Low Profile Separator/Trap