Kenco Engineering Weld Pad Flat Glass Level Gauge - Manual (Page 4)

Page 4
E. Reassembly Guidelines
NOTE: See the section on “GAUGE CONSTRUCTION” for the location any parts discussed below.
Kenco gauges use molded borosilicate glass, tempered to increase its bending resistance. This glass has a low
coefficient of expansion and is more resistant to thermal shock than other glasses. Nevertheless, like any glass it is
much stronger in compression than it is in tension. You should be careful not to impose any bending on the glass, or
set up any local stresses. The following points should be observed to insure long life:
• Check with the Maintenance Supervisor or Engineer for the proper glass to be used in the gauge. Check
box and glass labels or marking against the gauge pressure and temperature ratings.
• The glass, gaskets, cushions, and screws should not be reused, even when they appear in perfect condition.
Replace with new parts. Bolts will stretch when re-torqued, thereby weakening them. Glass deforms under
pressure from the chamber and cover. Even though a used glass may look perfect, it is not as reliable as a
new one. Best practice is to always use a new glass.
• The glass should be seated on a flat surface with a suitable gasket on the seating surface to avoid
subjecting the glass to stress concentrations which result from poor loading. It should be clamped in place
with a flat cover plate that is uniformly loaded, as described in the “Reassembly Procedures” below.
• The glass should not be in contact with any metal surfaces.
• For transparent gauges used in steam service, use mica shields between the glass and gasket on the
chamber (process) side.
F. Reassembly Procedure
To avoid leakage and undue stresses on the glass, we recommend the following reassembly procedure:
1.) Before reassembly, clean the gauge chamber seats and cover seats thoroughly with a soft metal scraper,
preferably brass. Be sure all burrs and bits of old gasket are removed. Gouged or scarred seats should be
refinished in a milling machine (or you can return the chamber to Kenco for refinishing). Damaged seats cause
low gasket compression and leakage.
2.) Locate the glass centrally in chamber and cover seat, to avoid glass-metal contact at the ends or sides. Use a
rubber band around the sides and ends of the glass. This will prevent glass-metal contact during assembly.
3.) With a torque wrench, replace the gauge covers as follows:
a.) Clean bolt threads, and apply a light oil to the threads and nut face. For gauges operating at more than
150°F, use Molykote or a similar molybdenum disulfide lubricant.
b.) Tighten the nuts finger-tight in the sequence shown in the “ASSEMBLY INSTRUCTIONS”, and then tighten
with a torque wrench in the same sequence. Tighten the nuts in five-pound stages. This procedure
produces even loading of the glass.
c.) Recommended final torque values: 25ft./lbs.
d.) New rubber-bonded gaskets tend to become permanently compressed after a short time in service. This
causes slight leaks or apparent loosening of the bolts. Therefore, re-torque to the original value after the
gauge has been in service for a few hours, using the same sequence as before.