Conax Technologies PG Packing Glands: Complete Technical Guide

Overview of Conax Technologies PG Packing Glands

The Conax Technologies PG-series packing gland is the industry-standard pressure-sealing fitting used in sample probe assemblies, thermocouple installations, and other instrumentation penetrations where a tube, rod, or wire must pass through a pressure boundary. Manufactured by Conax Technologies (now part of Ametek), these glands have been trusted by process engineers for decades in oil and gas, refining, chemical processing, and power generation applications worldwide.

The PG gland works on a simple but effective principle: compressible sealant elements are captured in a bore around the probe tube, and a threaded follower nut compresses those elements to create a leak-tight seal against both the tube OD and the gland bore ID. This design allows the tube to be inserted, retracted, or repositioned while maintaining the pressure seal — a critical advantage for retractable sample probe assemblies.

PG Model Range: PG2 Through PG9

Conax designates its packing glands by a "PG" number that corresponds to the body size, NPT thread, and the range of tube outside diameters the gland can accommodate. The table below summarizes the complete PG-series lineup:

The most commonly specified models for sample probe assemblies are the PG3 (for 1/4" OD probes), PG4 (for 3/8" and 1/2" OD probes), and PG5 (for 1/2" OD probes in larger process connections). The PG4 with 3/4" NPT threads is arguably the single most popular packing gland in the pipeline sampling industry due to its versatility and widespread availability of matching weldolets and threadolets.

NPT Sizes and Process Connections

Each PG model is designed for a specific NPT (National Pipe Thread) male thread that screws into a corresponding female NPT fitting on the process pipe. Common process connection types include:

• Threadolets: Welded branch connections with internal NPT threads; the most common connection for sample probes on pipelines
• Weldolets: Similar to threadolets but may require additional machining for NPT threads
• Couplings: Welded half-couplings with NPT threads, used on vessels and smaller pipe sizes
• Flanged adapters: For applications requiring flanged connections; adapter flanges convert the NPT gland to an ANSI/ASME flange face

When specifying the gland, the engineer must match the NPT size to the process connection already installed (or to be installed) on the pipe. Mismatching thread sizes is not possible without an adapter, and adapters introduce additional potential leak paths.

Sealant Options

The sealant element is the heart of the packing gland. Conax offers three primary sealant materials, each suited to different temperature ranges and chemical environments:

Teflon (PTFE) Sealant — Standard Service

• Temperature range: -350 degF to +500 degF (-212 degC to +260 degC)
• Chemical compatibility: Excellent resistance to virtually all chemicals except molten alkali metals and fluorine gas
• Pressure rating: Full rated pressure across the temperature range (derated above 400 degF)
• Best for: General-purpose oil and gas, natural gas pipelines, petrochemical, water, steam below 500 degF
• Designation: Standard (no suffix or "T" suffix in part number)

Teflon is by far the most commonly specified sealant for pipeline sampling applications. It provides a reliable, long-lasting seal and is compatible with hydrocarbons, H2S, CO2, amines, glycols, and most process chemicals encountered in midstream and downstream operations.

PEEK (Polyetheretherketone) Sealant — High Temperature

• Temperature range: Up to +600 degF (+315 degC)
• Chemical compatibility: Excellent resistance to most chemicals; superior to Teflon at elevated temperatures
• Pressure rating: Full rated pressure up to 500 degF; derated above
• Best for: High-temperature steam sampling, refinery process streams, power generation applications
• Designation: "K" suffix in part number

PEEK sealants are specified when process temperatures exceed the practical limit of Teflon (approximately 450-500 degF continuous). PEEK maintains its mechanical properties and sealing force at temperatures where Teflon would creep and lose compression.

Grafoil (Flexible Graphite) Sealant — Extreme Temperature

• Temperature range: Up to +1,000 degF (+538 degC) in non-oxidizing environments; up to +850 degF in oxidizing/steam service
• Chemical compatibility: Excellent in reducing atmospheres; may oxidize slowly above 850 degF in air
• Pressure rating: Typically derated compared to Teflon at a given gland size
• Best for: High-temperature superheated steam, furnace penetrations, extreme thermal cycling
• Designation: "G" suffix in part number

Grafoil is specified for the most demanding high-temperature services. It can handle thermal cycling better than polymer sealants and is the go-to choice for power generation steam sampling and high-temperature refinery applications.

Body Materials

Standard Conax PG glands are manufactured from 303 stainless steel (body and follower nut), which provides good corrosion resistance for most industrial environments. However, alternative body materials are available for special requirements:

For oil and gas applications involving sour gas (H2S concentrations above the NACE threshold), the gland body material must comply with NACE MR0175 requirements. This typically means specifying 316 SS in the solution-annealed condition with hardness not exceeding 22 HRC.

Torque Specifications

Proper torquing of the packing gland follower nut is essential for achieving a reliable seal without damaging the sealant or the probe tube. Under-torquing results in leaks; over-torquing can extrude the sealant, score the tube, or make future adjustment difficult.

Conax provides torque specifications based on gland size and sealant type:

Important: These values are guidelines. Always refer to the Conax installation instructions shipped with the specific gland, as torque values may vary by sealant element count and tube OD. After initial torquing, it is best practice to pressurize the system and re-torque if any leakage is detected, increasing torque in small increments (5 ft-lb steps) until the seal is achieved.

Replacement Sealant Elements

One of the key advantages of the PG gland design is that sealant elements are field-replaceable. Over time, sealant elements may wear, creep, or become damaged by thermal cycling. When this occurs, the follower nut is backed off, the old sealant is removed, new sealant elements are inserted, and the follower is re-torqued.

Conax supplies replacement sealant kits identified by the gland model number and sealant type. Keeping spare sealant kits on hand is recommended to minimize downtime during maintenance events.

Selecting the Right PG Gland

When specifying a PG packing gland for a sample probe assembly, the engineer must consider:

1. Tube OD: This determines the minimum gland size (e.g., 3/8" OD tube requires at minimum a PG4)

2. Process connection NPT size: Must match the installed weldolet or threadolet

3. Operating pressure: Must be within the gland's rated pressure for the selected sealant and temperature

4. Operating temperature: Determines sealant selection (Teflon, PEEK, or Grafoil)

5. Process chemistry: Determines body material (standard 303 SS vs. NACE-compliant 316 SS vs. exotic alloys)

6. Material compatibility: Ensure no galvanic corrosion issues between gland body and probe tube materials

The PG packing gland product page provides detailed specifications and ordering information for the full range of Conax PG-series fittings. For assistance with non-standard configurations, custom lengths, or exotic materials, contact our engineering team.