Other Flat Glass Gage Accessories
Gage Glass Shields
Mica Shields are used with process media that will corrode glass. The most common is steam above 2069 KPaG (300 PSIG) Working Steam Pressure (WSP). Transparent glass must be used to provide a flat surface to back the shield. Mica is a laminate type, naturally occurring material resistant to alkaline and can be used in high temperatures. As a layer of mica degrades in service, a new layer is exposed.
PCTFE (Formerly Kel-F) Shield
PCTFE shields are a common alternative to mica shields and extremely resistant to chemical corrosion but ineffective in steam service. These shields are most commonly used in hydrofluoric acid service. It should be noted that PCTFE is available in varying degrees of optical quality. While a PCTFE shield is not completely transparent, Jerguson shields are extremely clear and contain a minimal milky-white appearance. This milky-white appearance is prevalent with third-party product and can make it extremely difficult to read the level in the gage.
Belleville Spring Washers
Jerguson Belleville Spring Washers are recommended for process temperatures over 500°F (260°C) or 600# steam. Belleville Spring Washers help maintain constant bolt load during thermal expansion and contraction, thereby maintaining both gasket load and an effective seal.
Spring washers are installed between the nut and the bolt on reflex and transparent glass gages. Their contoured shape assists in adding tension to the bolt when installed. The added tension maintains the proper torque for a longer period of time.
Spring Washers are highly recommended when the gage is hard to get to. This can be due to insulation of the gage, difficulty seeing the gage if it is on a platform, or maybe it is hard to access the gage regularly. In these cases, spring washers will increase the reliability and extend the time between duty cycles.
Proper torque on the gage keeps all pieces tight together to prevent the gage from leaking. Proper torque will increase the life cycle of the gage. The best practice upon receiving a gage is to re-torque before installation, as the vibration from movement during shipping can loosen the bolts. In high temperatures, the best practice is to hot torque the gage. With the addition of spring washers, the hot torque between duty cycle changes can be extended.
Jerguson Support Brackets are typically recommended for gages in excess of four or five sections in length. This length recommendation can vary based on gage type (reflex or transparent) and the amount of piping between the glass level gage and the vessel.
Jerguson Expansion Loops relieve piping stresses which can be transmitted to the gage thru thermal expansion and contraction of the vessel. Expansion loops are typically recommended for steam applications above 750 WSP.
Required for cryogenic installations, should extend 1/2″ (12.7mm) beyond insulation
Reflex or Transparent Types
Standard or Large Chambers
For low temperature applications where frost has a tendency to build up on the gage, the Jerguson frost preventing unit keeps frost from covering the window and maintains clear visibility at all times.
The Jerguson Non-Frosting Unit consist of a plastic extension which makes direct contact with the gage glass and extends beyond the cover so that the frost build up does not obscure reading of the liquid level.
Mounting of the plastic extension is simple and can be accomplished without dismantling the gage. The non-frost extension can be installed or removed (for cleaning), either before or after the gage has been put into service.