ML18047A455
| ML18047A455 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 06/29/1981 |
| From: | TARGET ROCK CORP. |
| To: | |
| Shared Package | |
| ML18047A442 | List: |
| References | |
| 3069, NUDOCS 8207160350 | |
| Download: ML18047A455 (9) | |
Text
COPY NO.
PRESSUP.IZER SAFETY VALVE JUSTIFICATION REPORT PER EPRI LET"rER, JUNE 4, 1981 REPORT NO.
PROJECT NO.
3069 DATE 6/29/81 TOTAL PAGES 7
TARGET ROCK CORPORATION EAST FARMINGDALE. LONC ISLAND; N. Y.
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1.0 INTRODUCTION
Three Model 69C self-actuated pilot operated pressure relief valves*are currently employed. in nuclear power plant service.
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Duquesne Light Co Plant Beaver Valley l Valve Model 69C Drawing Number 69C-OOO Revision 7
2.0 DESCRIPTION
OF THE BASIC VALVE MODEL 2.1 General The Target Rock Model 69C Pilot operated relief/safety valve consists of two principal assemblies - a pilot valve section, and the main valve section. These two sections are directly coupled. to. provide a unitized, sel~-actuated relief/safety valve.
The pilot valve section is the pressure sensing and control element, and the main valve is a hydraulically (system fluid) actuated follower valve which provides the pressure relief function.
Operation-of the pilot and main valves is described in detail in the following sections. A schematic of the valve is presented in Figure I.
2.2 Pilot Section (Refer to Figures I, *rI and III)
The pilot section is a relatively small, tow-flow pressure sensing element which actuates the ma.in valve.
The key element of the pilot valve is the ma.chined bellows which acts as a combination piston, spring and hermetic seal.
As shown in Figure I.,
t:he top of the bellows is connected f~Y *OST l 1093
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a & I' o a T PaOJ&CT to the pilot valve disc thru a stem and disc yoke, between which there is au adjustable clearance or *vabutment gap"..
Operation of the pilot valve is as follows:
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During assembly, the bellows is mechanically extended a slight amount to provide a preload force on the pilot valve disc which seals the disc tightly>> and prevents reverse leakage at low system pressure or high pressures.*
- 2. In operation, as system pressure increases to Pl, the preload force is reduced to zero.
From. this point, the pilot valve disc is held closed by the internal pressure acting over the p~lot ~alve seat area.. This hydraulic seating force inc:reases with '
increasing system pressure, and prevents leakage or n~limmeriagn at pnssw:es near the valve set pressureo 3o As system pressure further increases, bellows expauq sion reduces the abutment gap between the stem and disc yokeo When the stem abuts against the yoke P2, further pressure increase reduces the net pilot seating force to zeroi and lifts the disc from its seato
- 4. At P3, ehe piloc valve starts to open, the hydraulic seating force is eliminated>> resulting in a net in-crease in the force, tending to open the pilot valve, This increase in net force, produces the popping action during pilot valve opening.
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3069 raOJICT AP'P'ROYfD *Y 2.3 Main Section Operation of the ma.in valve is as follows:
- l. In its normally closed position, the main valve disc is tightly seated by the combined forces exerted by the main valve preload spring, and tne system internal pressure acting over the area of the ~..ain valve disc.
- 2.
When system pressure increases to the pilot valve set pressure, the pilot valve will open; thereby admitting fluid pressure above the main valve piston.
This flow creates a differential pressure across the main valve piston in a direction tending to open the the valve. The main valve piston is sized such that the resultant opening force is greater than the combined preload and hydraulic seating force.
There-fore, opening of the*pilot opens the main valve.
- 3. As in the case of the pilot valve, once the main valve disc starts to open, the hydraulic seating force is reduced, causing a significant increase in opening force, and the characteristic full opening or "popping" action.
- 4.
When the pressure has been reduced sufficiently so that the pilot valve closes, leakage of system fluid
_past the main valve piston decreases the pressure over the piston, eliminates the hydraulic opening force, and permits the preload spring to close the valve. Once r:, ~ PO ST E 1 0 *3 I
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- &Poat' 3069 P&OJ&C:T closed, the addieional hydraulic seating force. due to system pressure acting on the main valve disc seats the main valve tightly, am prevents leakageo s *. Alarm Pressure Switch An alal:m pressure switch is mounted on the bonnet cap., '!his is pre*set ta activate an alarm in the event of a bellows rupture. A pressure build-up of 45 P.,S.I., in the baanet, will activate the alarme 3.0 SELEC'rED TEST VALVES The valves selected for EPRI testing were manufactured in 1980 to the original Model 69C drawings since no spare valves were ~vail.able9 4e0 DESIGN VARIATIONS BE'l'WEEN PWR PI.ANr VALVES AND SELECTED ?EST VALVES The test valves are identical ta those installed at Beaver Valley.
5.0 CONCLUSION
Inasmuch as the test valves were manufactured to the orlgi:cal Madel 69C drawings, they represent all the installed pressurizer safety valves of this type..
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Outlet Ma in Valve Preload Spring Main Valve Oise (Closed)
High Pressure Fluid Inlet MODEL 69C Abutment Gap FIGURE I Valve Schematic (Closed)
Page No.
5 of 7 Report No.
3069 Project:
Pilot Valve Di SC (Closed)
Yoke ~rtion of Pilot Valve Disc
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.1 Pilot Preload and Set Point Adjustment Spring Sensing Port
Outlet High Pressure Fluid MODEL 69C I
'Gap Inlet FIGURE II Abutmen...___
(Closed)
Valve Schematic (Open)
Page No.
Report No.
Project:
6 of 7 3069 Pilot Valve Disc (Open)
Ma in Valve Di SC (Open)
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