GLOBE VALVES OS & Y - FORGED - ISO 15761/API 602/B16.34
Australian Pipeline Valve - Installation, Operation and Maintenance Manual
14
Under no circumstances should the back seat be used to allow gland packing
replacement or repair while the valve and system are pressurised.
One of the most common misunderstandings is to believe that is the Globe valve is
back seated (fully open position - and backseat sealing made), this will help to
prevent wear of the packing rings. Unfortunately using the back seat in this way
over a longer period of time, could result in some serious issues:
a) Since the body, bonnet, stem and disc heat up and expand at different rates,
experience shows that valve can get jammed/blocked in back-seated position.
b) The gland packing will dry out faster since it’s not exposed to the media, and
could immediately blow upon closing of the valve.
To avoid this, once the valve is brought into fully open position (back seated), turn
the handwheel back on full turn.
Prior to replacing the packing rings, remove all pressure from the valve.
WARNING: If the backseat faces have been damaged by foreign material the
backseat may leak into the packing chamber.
3.3 PACKING REPLACEMENT
Ensure the line pressure is totally isolated prior to attempting to repack valve in-line. Wear anti-splash
eye protection goggles. See Caution below, do not attempt to repack the valve in line if dangers noted
applies as even if the valve is isolated there can be media trapped in the valve or line. Australian Pipeline
Valve graphite or PTFE and graphite packing sets have a diagonal cut that will allow them to be installed
around the stem of an assembled valve. However, the factory installed intermediate graphite packing
rings are sometimes die formed and have no end cut. As a result, these rings cannot be replaced without
removing the valve bonnet. If the valve is to be repacked without removing the bonnet, care must be
taken when removing the original packing not to scratch the valve stem sealing surface. Where it is
necessary to repack the valve in-line, a compatible ribbon packing system or equivalent braided packing
stock should be used. The joints in the packing rings should be diagonally cut. When installing the rings,
care should be taken to stagger the packing rings. See Figure 6. Refer to Section 4.2.1 for full packing
replacement procedure.
In the case of dangerous, hazardous, volatile, caustic or flammable liquids or gases,
it is dangerous to attempt to repack the valve in-line even if pressure has been
isolated. Never attempt any metal scraping, scratching or machining which as this
can cause inflammable liquids to ignite or personal chemical injury.
Other specialty packing such as V-ring Teflon may require that the valve be disassembled if repacking is
required.
