Seepex BN 5-12 Series, Руководство по эксплуатации и техническому обслуживанию

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Proper Use & Installation
Of Valve and Fitting Union Connections
TECH-2-No.109
TECHNOLOGY UPD
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TECHNOLOGY UPD
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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 further assure satisfactory
performance of plastic union connections.
Union Function Basics
Sealing Mechanism
- An internal O-ring is the sealing mechanism for a union connection. This seals in
two ways. On 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
fl uid using the pressure to create a tighter seal,
blocking fl uid medium from escaping between the mating components. This seal remains effective as long
as there is suf fi cient compression on the O-ring and will be compromised only when an operational situation
causes loss of compression.
Tightening – Tightening is only required to suf fi ciently compress the O-ring. Many suitable union connections
can be made with hand tightening of the Union Nut and an additional 1/16-turn of the nut with a strap wrench.
However, 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 union connection itself.
Typical Connection Problems
System Misalignment
- Failure to adequately seal a union connection is frequently attributable to
misalignment in system components, where the nut is used to forcibly draw together the End Connector and
Body Components. Misalignment may not allow even compression of the O-ring and results in loss of sealing.
Additional tightening applies undue stress to the threaded components that can potentially lead to fracturing.
Dirt & Debris – An often-overlooked problem, the simple presence of sand, dirt and debris on the O-ring or
mating surface can easily prevent proper sealing. Such can also cause dif fi culty 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 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.
Signi fi cant Temperature Variations
– Signi fi cant changes in either fl uid or ambient temperatures, including
sun exposure, can result in stretching of thermoplastic nuts. This “relaxing” in turn reduces O-ring compression
that can require additional tightening after initial installation.
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