The term commonly used in sealing engineering for an arrangement that applies a pressureless external medium (fluid, vapour, gas) to a mechanical seal's faces on the atmosphere side. A quench is used on the one hand when a single mechanical seal does not function at all or only within certain limits without auxiliary measures, and on the other hand when a double mechanical seal with pressurized buffer medium is unnecessary. The quench performs at least one of the duties described below; the numbers in brackets refer to the types of installation suitable for the given duty (the recommended installation is cited first), which are detailed in the following section.

Fluid quench

• Absorption (2,1) or removal (3) of leakage by the quenching medium
• Monitoring of the mechanical seal's leakage rate by periodic measurement of the level of the quenching medium in the circulation vessel (2) or thermosyphon vessel (2)
• Lubrication and cooling of the standby mechanical seal (1)
• Exclusion of air: For media which react with atmospheric oxygen in an undesirable manner, the quenching medium stops the leakage making contact with the atmosphere (3,2,1)
• Protection against dry running: For applications subject to brief, process-induced undershooting of the vapour head and brief operation of pumps without liquid (submersible pumps) at the mechanical seal, the quenching medium prevents dry running of the mechanical seal (3,2,1)
• Stabilization of the lubrication film: For operation under vacuum and/or sealing pressures close to the vapour head, the quenching medium stabilizes the lubrication film (2,3,1)
• Cooling (2) or heating (3) of the side of the mechanical seal facing away from the product

Vapour quench (3)

• Heating: For media with a high solidifying point the vapour quench prevents the leakage from solidifying in that area of the mechanical seal critical for its proper functioning
• Exclusion of air
• Removal of leakage

Gas quench (3)

• Icing protection: With operating temperatures below 0° C (cryogenic mechanical seals), the injection of nitrogen or dry air into the seal cover prevents the mechanical seal parts on the atmosphere side from icing up
• Exclusion of air
• Removal of leakage

Depending on the given duty, the quenching medium seal takes one of the following forms:

• Throttle bushings – the preferred choice for gaseous and vaporous quenching media, rarely for liquids
• Pro-stuffing boxes – the preferred choice for vapour, less often for liquids
• Radial shaft lip seals – the preferred choice for oils and water
• Mechanical seals – the preferred choice for all circulating quenching fluids (cf. also tandem mechanical seals).

1. Dead-end quench

Frequently this consists of a transparent, ventilated reservoir positioned directly above the seal casing. With a vertical shaft, the space above the mechanical seal performs the function of the quench reservoir (cf. submersible motor pump). Quenching medium – preferably oil; API 610 recommends methanol.

No. 13  .. quenching fluid from an elevated reservoir

2. Circulation

Circulation of quenching medium via a pressureless reservoir. Quenching medium – any suitable fluid.

No. 10  ... quenching fluid from an elevated reservoir; circulation of fluid by thermosyphon effect or by a pump system.

Plan 54 Circulation of clear fluid from externa system

3. Throughflow

The quenching medium flows through. Quenching medium – fluid, vapour, gas.