Sample Valves

Overview

Valves in a sample conditioning system serve two fundamental functions: isolation and flow control. The wrong valve selection introduces dead volume, creates particle traps, causes sample contamination, and degrades analytical accuracy. In trace-level analysis, even minor valve deficiencies can produce measurement errors that lead to incorrect process control decisions or compliance violations.

Our sample valve offering covers the two primary valve types used in analytical sampling: ball valves for positive shutoff and isolation, and needle valves for precise flow regulation and throttling.

Ball Valves

Function and Application

Ball valves provide quarter-turn on/off isolation with full-bore flow paths that minimize dead volume and pressure drop. In sampling systems, they are used for probe isolation, sample point shutoff, bypass valve service, and block-and-bleed configurations. The swept-volume design reduces the risk of sample carryover between operations.

Available Configurations

Sizes:

• 1/4" tube OD (compression or weld end)
• 3/8" tube OD (compression or weld end)
• 1/4" and 3/8" NPT female threaded versions also available

Materials of Construction:

• 316 Stainless Steel -- Standard for most hydrocarbon and chemical sampling applications
• Alloy 400 (Monel) -- HF service, reducing acid environments
• Alloy C-276 (Hastelloy) -- Severe chemical service, chloride environments
• Carbon Steel -- Low-cost option for non-corrosive utility service

Pressure Ratings:

• 1/4" tube: up to 6,000 psig CWP (316SS)
• 3/8" tube: up to 6,000 psig CWP (316SS)
• Ratings derate with increasing temperature per ASME B16.34

Seat and Seal Materials:

• PTFE seats for general service (-65 degrees F to +450 degrees F)
• PEEK seats for high-temperature service (up to +550 degrees F)
• Metal-to-metal seats for extreme temperature or fire-safe requirements

Handle Types:

• Lever handle -- Standard quarter-turn operation with visual open/closed indication. Most common for accessible installations.
• Oval handle -- Low-profile design for panel-mounted systems and enclosures where lever clearance is limited.
• Lockout handle -- Equipped with a lockout/tagout hole for safety compliance in permit-required isolation points.
• T-handle -- Compact grip for high-density valve manifold installations.

Key Specifications

Needle Valves

Function and Application

Needle valves provide fine flow control through a tapered stem that seats into a precision-machined orifice. In sampling systems, needle valves regulate sample flow rate to the analyzer, control bypass flow, and serve as calibration gas isolation and metering valves. Their graduated adjustment capability is essential for maintaining consistent sample flow rates at the low flow conditions typical of analyzer installations.

Available Configurations

Sizes:

• 1/4" tube OD (compression end)
• 3/8" tube OD (compression end)
• 1/4" and 3/8" NPT female threaded versions also available

Materials of Construction:

• 316 Stainless Steel -- General-purpose process sampling
• Alloy 400 (Monel) -- HF acid and reducing environments
• Alloy C-276 (Hastelloy) -- Aggressive chemical and chloride-bearing streams
• Alloy 625 (Inconel) -- High-temperature flue gas and furnace sampling

Pressure Ratings:

• Up to 10,000 psig CWP at ambient temperature (316SS, 1/4" tube)
• Up to 6,000 psig CWP at ambient temperature (316SS, 3/8" tube)
• Ratings derate with temperature per valve manufacturer tables

Stem Types:

• Non-rotating stem tip -- Prevents galling and seat damage during throttling. Recommended for frequent adjustment service.
• Regulating stem -- Vee-point tip for precise, linear flow control. Preferred for sample flow metering applications.
• Integral bonnet -- Welded bonnet design eliminates a potential leak path. Specified for toxic or hazardous service.

Valve Selection for Sample Integrity

Proper valve selection directly impacts the quality and representativeness of your analytical sample. Consider the following when specifying valves for sampling systems:

• Minimize dead volume. Select full-port ball valves and straight-through needle valve bodies to eliminate pockets where old sample can accumulate and contaminate new readings.
• Match materials to the process. Corrosion products from an incompatible valve body introduce contaminants that interfere with trace-level analysis.
• Consider wetted surface finish. For trace sulfur, moisture, or reactive gas analysis, specify electropolished or SilcoNert-coated valve internals to prevent adsorption and desorption effects.
• Specify appropriate end connections. Compression fittings are standard for field installations. Weld ends are preferred for permanent, zero-leak connections in critical or hazardous service.
• Account for maintenance access. Lever-handle ball valves provide clear visual indication of valve position, reducing the risk of operator error during sample system maintenance.

Ordering Information

Specify the following: valve type (ball or needle), size, end connection type, body material, seat/seal material, pressure class, and handle type. For panel-mounted systems or custom manifold configurations, contact our engineering group for assistance with valve layout and specification.