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Proper use and installation of Spears valve and fitting union connections

Proper use and Installation of Spears valve and fitting Union Connections

Union connections provide a removable joint that allows assembly and disassembly for temporary connections or installation of piping, valves, and other equipment that may need to be removed from a system for servicing or replacement. While simple in operation, understanding a few details will ensure satisfactory plastic union connections' performance.

Sealing Mechanism - An internal o-ring is the sealing mechanism for a union connection. This seals in two ways. At an initial installation, the O-ring must be compressed enough to effect a seal between the mating surfaces of the body and end connector components. This is accomplished by tightening the union nut. Secondly, as pressure increases, the O-ring moves with the fluid, using the pressure to create a tighter seal, blocking the fluid medium from escaping between the mating components. This seal remains effective as long as sufficient compression on the O-ring and will be compromised only when an operational situation causes loss of compression.

Tightening – Tightening is only required to sufficiently compress the O-ring. Many suitable union connections can be made by hand-tightening the union nut and an additional 1/4 turn of the nut with a strap wrench. Care should be taken to avoid over-tightening! Additional stress imposed can potentially damage components. The necessity for additional tightening is generally an indication of other problems within the system or the union connection itself.

Typical Connection problems

System Misalignment – Failure to adequately seal a union connection is frequently attributed to misalignment in systems components, where the nut is used to forcibly draw together the end connectors and the body components. Misalignment may not allow even compression of the O-ring, resulting in loss of sealing. Additional tightening applies undue stress to the threaded components, potentially leading to fracturing.

Dirt & Debris - An often overlooked problem, the simple presence of sand, dirt, and debris on the O-ring of mating surfaces can easily prevent proper sealing. Such can also cause difficulty in tightening the nut if threads are clogged.

Damage to O-ring or mating Surfaces - Much like the effect of debris, damage to the O-ring or union components can prevent proper sealing by either not allowing proper compression or creating a leak path under the O-ring seal.

Lubricant Use – Certain lubricants are stress-cracking agents that can induce premature failure of components, especially the nut, under normal tightening stress loads. A properly installed union connection should not require lubrication to assemble. The perceived necessity of a lubricant is also indicative of other problems.

Significant Temperature Variations – Significant changes in wither fluid or ambient temperatures, including sun exposure, can result in the stretching of thermoplastic nuts. The "relaxing," in turn, reduces O-ring compression that can require additional tightening after initial installation.

Essential Installation Instructions - Preparation Checks

  • Check that pipe ends are properly prepared for solvent cement or threaded installation of end connectors
  • Check that the system has the adequate free movement for the final assembly of Union Connection without misalignment or the need to "draw together" any gaps.
  • Check that valves and system have adequate support

Install End Connectors

  • Always remove the union Nut and End Connector for valve installation.
  • Slide Union nut onto pipe BEFORE installing End connector.
  • Spears® Uses a retained (press-fit) O-ring on the End connector. Check that the O-ring is in place and pressed evenly into the groove without bumps or ripples.
  • Solvent cement or thread End connectors to pipe as applicable. Allow to cure before further assembly or valve installation.

Install Union Connection

  • Make sure that the face of the end Connectors is squarely aligned with the face body and flush against the O-ring. DO NOT USE UNIONS NUTS TO DRAW TOGETHER ANY GAPS OR TO CORRECT SYSTEM MISALIGNMENT.
  • Support assembly and thread union nut onto the body.
  • Tighten nut hand tight only.
  • DO NOT use Metal pipe wrenches.

Adjustments after Pressure Tests

  • If any leaks are detected during the systems pressure test, disconnect the union and check for noted problems; then reinstall. If the problem persists, tighten the union no more than an additional 1/16 turn. Use ONLY strap wrenches. Apply a reference mark to the nut and body as an index to avoid over-tightening. Tightening must not exceed the following maximum torque values:
Union Size


  • Do not use lubricants or thread sealants on union nuts.
  • Do not use union nuts to draw any gaps or correct system misalignment.
  • Do not support equipment or system components from a union connection.
  • Do not use any metal wrenches. Use only strap wrenches.
Title: Proper use and installation of Spears valve and fitting union connections
Description: Information on installing Spears Union Connections.
Published: 6/2/2008
Last Edited: 1/20/2023
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