281.491.2331 13839 West Bellfort Street Sugar Land, Texas
281.491.2331 13839 West Bellfort Street Sugar Land, Texas
ISO 9001:2015
U.S. Patents
90 + U.S. Patents
Since 1954
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Superior Natural Gas Sampling System

No autographs, please. The unrivaled accuracy of Welker’s GSS-4PM Gas Sampling System is world-famous. Its unparalleled decades-long history of representative sampling, repeatability, and accuracy have made the GSS-4PM the composite sampling system for natural gas—wet or dry, clean or dirty.

Probe-mounted and self-purging, the GSS-4PM is a self-contained system compatible with single cavity and constant pressure cylinders. With the Vanishing Chamber™ collection cup at the heart of the positive displacement pump, there’s no doubt your samples will be as representative and accurate as the results of an online analyzer.

Welker GSS-4PM
Complies WithGPA 2166, API 14.1, ASTM D5287, ISO 10715
Vanishing Act

Unique Collection Head

The GSS-4PM’s claim to fame is the Vanishing Chamber™ collection cup. This compressible collection cup captures set volumes of sample. Each actuation of the sample pump voids the collection cup, fully displacing the sample into the connected sample cylinder. Made from resilient material, the Vanishing Chamber™ bounces back to provide repeatable results actuation after actuation.

In the Short Run

Eliminate Lag Time

Mounted on a Welker Sample Probe, the GSS-4PM installs directly to the pipeline. There are no long tubing runs to impact sample timeliness and representativeness. Extending into the center one-third of your pipeline, the GSS-4PM captures samples representative of the flowing stream and leaves free liquids behind.

Total Knockout

Optional Liquid Eliminating Probe

For wet gas sampling applications, swap the standard Welker Sample Probe for a Welker LE-2SSKO. The patented design of our probe-mounted liquid eliminator effectively knocks free liquids out of the sample stream and returns them to the pipeline.

Fresh Off the Pipeline

Collect Representative Samples

The GSS-4PM features Welker’s Fresh Sample System™. This self-purging design ensures a fresh, representative sample grab during each sample cycle.

Clear the Way

Integrated Purge Manifold

Don’t let residual impurities distort your sample. Air or previous samples can impact sample accuracy if not properly removed. Purge your sample cylinder before each collection period as recommended using the GSS-4PM’s integrated purge manifold.

Without Interruption

Easy Maintenance

There’s no need to depressurize your pipeline and remove the GSS-4PM for standard maintenance. To safely remove the sample pump, simply close the valves on the probe base to isolate it from process pressure.

Point of No Return

Backflow Protection

The inline relief protects sample representativeness during fluctuations in pipeline pressure. Acting as a check valve, the inline relief keeps your samples in the sample cylinder. If pipeline pressure drops, rest assured sample won’t flow from your cylinder back to the pipeline.

Please Hold

Cylinder Holders Included

No need to add a cylinder holder to your order—each GSS-4PM comes standard with a manifold for a single cavity cylinder and a bracket with mounting hardware for a constant pressure cylinder. The manifold keeps your single cavity cylinder vertical for proper filling and purging. The bracket provides the horizontal support your constant pressure cylinder requires and keeps it close for short tubing connections.

Timing is Everything

Optional Timing System

When it comes to operating the solenoid, you have the power to choose. Connect the GSS-4PM to a Programmable Logic Controller (PLC) or other signal control system or select a Welker onboard timing system.

After connecting a 12- or 24-volt power supply, the optional Welker 4P Sample Frequency Controller can run on an analog or a digital signal. An optional converter keeps you up and running if your site doesn’t have a direct current power supply.

No external power supply? No problem! The long-lasting lithium battery pack of the optional Welker 6Tc Timer/Controller can power the GSS-4PM. This UL listed intrinsically safe controller is designed for hazardous areas.


GSS-4PM Composite Gas Sampler
Materials of Construction316/316L Stainless Steel
Seal MaterialViton®
Pipeline Connection 3/4" MNPT
Outlet Connection 1/4" FNPT
Collection CupViton® Vanishing Chamber™
Relief TypeInline Relief
Insertion Length8"
Sample Volume0.22 cc
BypassIntegrated Bypass Manifold with Built-in Valve
OperationDiaphragm-Operated Pump
Operating Pressure2160 psig MAOP @ -20 °F to 120 °F
Industry StandardsComplies with API 14.1, GPA 2166, and ISO 10715

Standard Options

GSS-4PM Composite Gas Sampler


Pipeline Connection


3/4" MNPT


Solenoid Only
Collection Cup




80 duro
Collection Cup Size


0.22 cc


2000 psig
Probe Length


Plus Welker

For custom options, choose Plus Welker™.

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Collaborate with us to create a custom product unique to your application.