8 | BHGE
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VIII. Introduction
Modern nuclear power plants have given rise to systems
which cycle extremely large quantities of steam at relatively
low pressures. This is particularly true in the reheat portion
of the turbine cycle.
These requirements have exceeded the feasible limits of
conventional spring loaded safety valves. In response to this
requirement, the Consolidated 13900 series pilot operated
safety relief valves were developed for ASME Code Section
VIII service providing discharge orifice sizes up to 200 square
inches with minimum overall height and weight.
The pilot senses pressure internally through the main valve
eliminating the need for external pressure lines which
normally are subject to mechanical damage, fouling or
rupture.
The combination of conventional spring loaded pilot and an
internal sensing tube meet all Code requirements for a Fail
Safe Device.
As an additional safety feature, the pilot discharge can be
vented to the outlet of the main valve if required. This is
accomplished by the use of a discharge tube from the pilot
valve outlet to the main valve outlet.
An effort has been made to provide a valve which requires
a minimum of maintenance upkeep and can be actually
repaired on its installation site.
Factors which contribute to minimum maintenance
requirements of the Main Valve consist of:
1. No metal sliding surfaces;
2. Use of Teflon seals for good high temperature sealing
characteristics.
3. Metal to metal load bearing characteristics of
Consolidated's O-Ring seat seal which will not deform
the seat seal anymore than required for pressure sealing.
When maintenance work is necessary, the following features
offer advantages in reducing the amount of labor required:
1. All parts of the valve are top inserted.
2. It is not necessary that the valve be removed from its
installation site or that the outlet piping be removed,
unless the seat bushing requires rework.
3. Large diameter soft seats do not require the"Excellence
of Technique" needed to get leakproof large diameter
metal seats.
4. The pilot valve can be removed and be reworked and
readjusted on a separate small test facility.
VII. Pre-Installation and Installation Instructions
1. Lift the valve using all three eye bolts located on the top
flange (See Figure 1, Item 26). Eye bolts must be fully
engaged in top flange.
CAUTION
Do not allow lifting chain or sling to exert any sideways
thrust on the pilot valve or damage to pilot valve will result.
