Spherical Valve Technical Description

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Nafra Hydro Electric Project (2 x 60 MW)Techno-Commercial Bid DocumentICB No. - SEW/NAFRA/E &M- Package - 2/09/2010

2 x 60 MW NAFRA HE Project

Technical DescriptionSpherical Valve as MIV Revision -

Technical DescriptionSpherical Valve as MIV

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Table of contents

1 Introduction.......................................................................................................................................... 3

2 Design Data.......................................................................................................................................... 4

2.1 Main Dimensions................................................................................................................................. 4

2.2 Operation Conditions........................................................................................................................... 4

2.3 Allowable stresses............................................................................................................................... 5

3 Design Features................................................................................................................................... 7

3.1 Valve Body (Housing).......................................................................................................................... 7

3.2 Rotor with Trunnions........................................................................................................................... 8

3.3 Valve Seals......................................................................................................................................... 9

3.3.1 Service Seal..................................................................................................................................... 9

3.3.2 Maintenance Seal............................................................................................................................. 9

3.4 Bearings............................................................................................................................................ 10

3.5 Valve Servomotor.............................................................................................................................. 10

3.6 By-Pass............................................................................................................................................. 10

3.7 Control and Monitoring...................................................................................................................... 10

3.8 Downstream Pipe with Dismantling Joint .......................................................................................... 11

3.9 Upstream Pipe................................................................................................................................... 113.10 Accessories..................................................................................................................................... 11

4 Shop Assembly and Tests.................................................................................................................11

5 Field Tests........................................................................................................................................... 12

6 Operation and Maintenance..............................................................................................................12

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1 Introduction

The Main Inlet Valve (spherical valve) will be installed upstream of the turbine inlet pipe in the

power house. The valve body will be bolted to the upstream pipe which will be welded at lower

end of the penstock. Downstream side will be connected to the turbine inlet pipe by a

dismantling joint. The valve body will be settled over embedded base plates and can slide

freely in axial direction to compensate pipe deflections due to the axial force when valve is

closed.

The spherical valve is a protection element of the Hydropower Plant and acts as an

emergency closing device in case guide apparatus fails to close the guide vanes and also in

case of any damage to the inlet pipe, Spiral case or any other element downstream of the

valve.The valve serves also as an isolating element, to drain the spiral case for inspection and

maintenance of turbine component(s) without the necessity of emptying the penstock.

Typical views / arrangements are provided in this document. However, exact details /

arrangements will be provided specific to the project during detailed engineering.

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1 Valve Body2 Counterweight3 Upstream pipe4 Dismantling pipe5 Valve Servomotor


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Typical

Spherical Valve Arrangement

2 Design Data

2.1 Main Dimensions

Nominal diameter DN 2200 mm

Design pressure PN 250.3 mwc

Test Pressure Ptest 375.5 mwc

Oil pressure rating p 80 to 120 bar

Maximum Discharge Qmax 40 m3/s

2.2 Operation Conditions

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Normal closing: By counter weights

Normal opening: By servomotor(s) oil pressure under no-flow & balanced

condition (closed wicket gates).

Emergency Closing: By counterweights under full flow condition. Also closing

under 200% of max discharge(As an extreme load case)

2.3 Allowable stresses

The following sections present some principal criteria for determining the dimensions of load

carrying valve components, based on stress levels and loading. It is divided in two paragraphs,

describing in paragraph a) the allowable stresses and in paragraph b) the definition of loading

cases for different valve components.

a) Allowable stresses

Adequate factors of safety will be used throughout the design. Under the most severe

conditions of loading expected in the various load cases, stresses in the material will not

exceed the values listed below. The values for uniform stresses apply for conventional

calculation methods, the values for peak stresses can be considered by means of finite

element calculations.

The allowable stresses are determined to the minimum yield point and consider local peak

stresses. The actual combined stresses have to be calculated according to the von Mises

Theory:

223 +=

V

and must not exceed the allowable stresses shown in the diagram below.

YieldKallowV

=

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b) Definition of load cases

Spherical Valve

Components

Normal Operation Severe Operation

Operating Loading

Cases

Exceptional

Loading Cases

Extreme Loading

Cases

Valve Body Max. static Head +

Water Hammer

Maintenance Seal

engaged (effective

Penstock Pressure with

Valve closed and other

Units facing Full Load

Rejection)

Pressure Test

Valve Rotor and

Trunnion

Effective Pressureduring closing at Max.

static Head at normal

Flow

Penstock Pressure with

Valve closed and other

Units facing Full Load

Rejection

Maintenance Seal

engaged (Penstock

Pressure with Valve

closed and other Units

facing Full Load

Rejection)

Closing under rupture ofPipe (200% of max

discharge)

Pressure Test with Rotor

closed (if no

downstream Test Head

foreseen)

Servomotor and Drive Closing under full Flow Pressure Test

Closing under Rupture

of Pipe (200% of max

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discharge)

Rotor blocked

3 Design Features

3.1 Valve Body (Housing)

The valve body will be in two parts and will be a integrally cast or cast welded or welded

design. The connection between the upstream and downstream parts of the valve body shall

be made with bolts of high strength steel utilizing rubber O-rings as sealing elements.

The body will have a tap on the highest point for aeration and an adequate flange connection

at the bottom for draining the valve for maintenance.

The body will have integral feets to support it on embedded base plate. To allow axial

movements of the housing, the feet will be equipped with an arrangement suitable for the

intendedservice.

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Typical Spherical Valve Design

3.2 Rotor with Trunnions

The valve rotor will be designed from cast steel and/or fabricated steel plate. It will withstand

the forces due to water pressure keeping the deflections to an absolute minimum.

The attached trunnions will be made of cast stainless steel. They will be attached to the rotor

by high strength steel bolts. Alternatively trunnion will be made with forged carbon steel with

stainless steel sleeve.

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Typical Rotor Design

3.3 Valve Seals

The spherical valve shall be equipped with two main seals, a service seal and a maintenance

seal. To attain sealing, the movable part of seals will be pressed to the stationary seat ring by

using penstock water through seal water control system. The movable parts are located in

body and stationary seat rings are on the rotor.

3.3.1 Service Seal

The service seal is arranged at the downstream end of the spherical valve. In the open

position of the rotor and during the closing motion the seal remains retracted by pressurized

water taken from the penstock through seal water control system. It will be ensured by

governing system that seal gets applied only when rotor is in closed position.

3.3.2 Maintenance Seal

The maintenance seal is arranged at the upstream end of the spherical valve. It permits

maintenance work on the service seal at the downstream end of the valve. It will be applied by

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a manually operated hydraulic valve utilizing pressurized water from the penstock. It will be

ensured by governing system that seal gets applied only when rotor is in closed position.

3.4 Bearings

The proposed bearings are maintenance free, with stainless steel mating surfaces on the

trunnions and bronze carrying bushings that can be exchanged with a minimum of

disassembly effort. The radial bearings and trunnion seals will be fitted inside carrier bushings.The trunnion seals are arranged to prevent water from entering the bearing.

3.5 Valve Servomotor

Opening of the valve is performed by two single acting hydraulic servomotors, which are

operated by pressurized oil from a hydraulic oil supply system. Closing weights are provided

for the closing of inlet valve. The valve servomotor will be designed to withstand the maximum

forces during emergency closure.

3.6 By-Pass

A by-pass pipe will be included from the upstream connecting pipe to the downstream pipe

extension of the valve. The bypass line shall also have one full flow guard valve for the bypass

valve. The bypass valve shall be slide valve with valve seat. It shall be operated hydraulically

(by servomotor) and be equipped with proximity switches indicating the open and closed

positions of the bypass.

3.7 Control and MonitoringFor control and monitoring purposes, the valve will be equipped with the following

instrumentation:

Penstock pressure gauge

Pressure gauge for pressure measurement on downstream side on valve

Valve rotor position indication (with scale, limit switches)

Pressure differential switches

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3.8 Downstream Pipe with Dismantling Joint

The downstream pipe is equipped with boss for bypass line connection. On upstream side, it has

welded flange for connection with valve body. On downstream side, it comprises of dismantling joint

with loose flange(s) which will be connected to spiral case inlet flange.

3.9 Upstream Pipe

The upstream pipe is equipped with boss for bypass line connection. Its downstream end haswelded flanges for connection with valve body and upstream side will be prepared to weld with

Penstock. It will be designed to transmit axial load to concreted thrust block when the valve is in

closed position.

3.10 Accessories

The following accessories will be supplied:

Pipe for drainage, including shut-off valve.

Air Release valve to release/ supply air.

Access platforms complete with stairs and guard-rails for access to operate/maintainarrangements on the top of the valve, e.g. bypass arrangement, etc.

4 Shop Assembly and Tests

The spherical valve will be assembled in the workshop without servomotor and counter weights. The

assembly will be filled with water, leakage tested at the maximum operating pressure and pressure

tested for integrity at 1.5 times the design pressure.

Function Tests:

The complete valve with testing levers excluding servomotors and counter weights

shall be assembled and tested in the workshop.

Operating test of the complete inlet valve.

Operating test of the servomotor separately for free movement for closing and

opening.

Operating test of bypass arrangement separately.

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5 Field Tests

Valve seals leakage test.

Operational tests to check sequence of operation of by-pass valve, valve seals, etc

as per approved logic diagram.

Closing under full flow condition.

Opening under pressure balanced condition.

Determination of valve opening / closing time.

6 Operation and Maintenance

Operation manuals and maintenance manuals will be provided before commissioning phase.

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Documents

Spherical Valve Technical Description