TRIP AND THROTTLE VALVE WITH HYDRAULIC MANUAL EXERCISER FOR STEAM TURBINES

Elliott

Ebara Turbomachinery Corporation

GENERAL

This valve has two major functions. One is for use as an emergency shut-off valve to

trip the turbine, and the other is to admit and throttle steam to the turbine during

manual start-up operation. The valve can be shut-off from local and / or remote by

operating oil release valve in the oil feed line. The hydraulic manual exerciser, one of

the important features, is furnished with the trip and throttle valve.

CONSTRUCTION

This valve consists of a globe type valve body with a balanced disk and stem, seal

bushings, handwheel, hydraulic piston and cylinder, two oil relay plungers / cylinder

and oil pilot relay.

1. Valve Disk

The forces exerted on the main spindle (12) by steam pressure are balanced. The

valve disk (8) and the cover (2) form the pressure balance chamber. The pilot valve,

integral with the main spindle, is enclosed in the valve disk with the valve cover (9).

When throttle the steam with the handwheel (26), the pilot valve open to balance the

pressure in the chamber with the pressure below the disk. So, the required force at

handwheel is reduced.

The steam strainer (4) installed in the casing is removable without dismantling the inlet

steam piping.

The orifice plug (83) can be furnished in the cover for adjustment of the steam pressure

in the chamber above the valve disk when the pilot valve is opened.

But as normally no orifice opening is necessary, a blind plug (83) is installed in the

shop. If the valve disk rattles excessively during opening operation, drill an

appropriately sized hole in the plug to adjust the pressure. Steam should be

completely shut off with an inlet block valve before removing the outside plug (84) for

orifice adjustment.

2. Sealing

The upper and lower bushings (15) (16) are furnished to minimize steam leakage and

to guide the valve main spindle (12). The upper bushing (15) is designed to lead

steam leakage away through the leak-off connection. Steam leakage through the

lower bushing is carried off from the connection in the closed void at the bushing end.

The back seats are used to minimize steam leakage through the upper bushing when

the valve is in the full open position.

3. Oil Cylinder and Trip Spring

The valve spindle is divided into two pieces, the main spindle (12) and an upper spindle

(17). The spindles are joined with a connection (22).

The upper spindle is guided by a bushing (38) and a sleeve (40). The handwheel (26)

is installed at the top of the upper spindle. The upper spindle can be turn in the

connection (22) and the sleeve (40). The rod (72) prevents the main spindle from

turning.

The spring (35) providing tripping force to the valve is furnished with the sleeve (40).

The sleeve rests on the piston (43) which is floating on the oil in the cylinder. During

normal operation, the oil in the cylinder supportins the piston at the upper end of the

stroke. Upon loss of oil pressure, the piston will lose it ’s supporting force and

consequently the valve is forced to trip (fully close position) by the spring. The spindle

(17) is threaded and meshes with a sleeve (40).

4. Oil Pilot Valve

To control the action of the piston (43), an oil pilot valve mechanism is furnished with

the oil cylinder. Oil is introduced to the valve through an orifice. The orifice shall be

installed in the oil feed line, separately from the valve. The size is shown in the valve

drawing. In the line between the orifice and the oil feed connection of the oil pilot

valve, an oil release valve, receiving a remote trip signal, is furnished.

If oil is not supplied or oil pressure is lost, the oil pilot valve piston (57) rests on the

bottom of the oil pilot valve cylinder (48). When the pilot valve piston rests there, oil

will flow through the piston to the oil drain connection and not provide supporting force

for the main piston (43), even if oil is supplied from the process line. The valve cannot

be opened in this condition.

To reset the valve, the handwheel should be turned clockwise. This operation lifts the

sleeve (40) to compress the spring (35). The lever (41) rises with the sleeve. During

this time, the piston (43) remains resting on the cylinder bottom. When the sleeve

reaches the reset position or passes the bottom end of the stopper (36), a lever (41)

and bar (81) raise the oil pilot valve piston (57) to choke the oil path through the pilot

piston to oil drain line. Consequently, oil pressure rises and forces the pilot piston (57)

to the upper end.

Now, oil flow is directed to the cylinder (31) through the orifice openings in the oil pilot

piston to raise the main piston (43).

After the main piston (43) settles at the end of the stopper (36), this trip and throttle

valve can be opened by turning handwheel (26) counter-clockwise. Now, manual

operation, opening, closing or throttling is possible with the handwheel.

5. Manual Exerciser

This trip and throttle valve is capable of being partially stroked to exercise the valve

without interrupting turbine operation.

When the handle (60) is pulled manually, the main piston (43) drops to the level of the

side hole below the manual exercise valve (59).

A check can be made to ensure that the parts move freely.

OPERATION

When starting the turbine, this valve can be used as a throttle valve to manually control

the turbine speed. The oil release valve in the oil feed line for remote trip should be

reset (close) first. This enable T&T valve reset.

Even if the oil release valve is reset, this trip and throttle valve will not move.

To reset the valve, the handwheel (26) should be first turned clockwise. This action

allows the sleeve (40) to rise. At the final stroke of the sleeve, the oil pilot valve piston

(57) is automatically reset. After approximately ten seconds, the main valve is ready

to open.

To open the valve, turn the handwheel counter-clockwise. To close or throttle the

valve, turn the handwheel clockwise.

To trip the valve, open the oil release valve in the oil feed line.

When the feed oil pressure drops below the specified trip pressure, the oil pilot piston

starts to move and the valve trips with further pressure drop.

Once the valve trips, it can not be opened without following the reset process described

ablve.

REMARKS

1. The handwheel should be turned approximately one half turn in the closing direction

from its wide open position to avoid binding. This is to prevent the piston from

locking the stopper.

2. To check valve movement, pull the handle (60). The valve moves partially.

Releasing the handle restores the valve to the full open position. This manual

exercising should be performed periodically to check that the parts move freely.

3. It is not recommended the valve be tripped from the full open position without the

specified inlet steam pressure. This may damage the valve disk and the seat

because of insufficient dash pot effect.

4. Steam should be completely shut off with an inlet block valve before overhaul the

valve.

5. Clean the built-in strainer at every turnaround. This strainer is not meant to function

as a constant steam screen. It is not capable of screening fine particles or large

amounts of debris but is only for protecting the valve and turbine from major damage

due to unexpected foreign matter. Steam should be sufficiently clean.

6. The valve should be overhauled when any malfunction is discovered.

LUBRICATION and MAINTENANCE

The connection (22) should be keep clean, be inspected and be greased periodically.

Grease should be properly fed as instructed in the assembly drawing.

DISASSEMBLY

Remove nuts of the cover (2). Then draw out the oil cylinder (31), the pilot valve

cylinder (48), the spindles (12) (17), the valve disk (8), etc. at the same time. Then

disassemble the handwheel (26), the cover (33), sleeve (40), the connection (22), the

nut (20). Disconnect the spindle (12) and the valve disk (8). If completed the

disassembly, inspect each parts and repair / replace defected parts if necessary.

REASSEMBLY

Reassembly is accomplished in reverse order to the steps outlined above. When

assembled, check the function of handwheel, trip mechanism, manual excerciser, etc.