FIELD OF THE INVENTION;
The present invention relates to a device for in situ lapping of turbine
valves, in particular the invention relates to lapping device for smooth
lapping of valve seats without removing the valve from installed position
for repairing purpose.
BACKGROUND OF THE INVENTION:
The components of valves of steam turbine are made in shop and they
are checked before despatch to erection side. But because of human
slippages, inadequate packaging, damage during transportations,
handling at site, valve seats of the valve can get damaged. Damaged valve
seats are vulnerable for use in regard to proper functioning of valves.
When valves are put in the turbine, it get assembled with the pipes of the
turbine. Once the valve is erected and the damage on valve seat is
noticed, it can not be left as it is without correction of the damaged seat.
At this stage the only option to repair is to take out the valve by cutting
the pipes and transporting it back to repair shop for repair by machining
or vertical lapping. The whole process is time consuming and costly
affair. This process also affects the commissioning schedule of new power

plants or increase the outages of the machine in the running power
plants.
There was therefore, a need for providing a method or repairing a valve
seat by lapping at site without the need of dismantling the valve and
sending it to the shop for repair. In known methods, the correction is
done at the repair shop.
OBJECTS OF THE INVENTION:
1) An object of the present invention to propose a device for in situ
lapping of valve of seat of turbine valves which eliminates the
disadvantages of existing state of Art.
2) Another object of the invention is to propose a device for in situ
lapping of valve seat of turbine valve which carries out the
lapping work at the place of work without removing the valve.
3) A further object of the invention is to propose a device for in
situ lapping of valve seat of turbine valve which saves huge
repairing time.

4) A still further object of the invention is to propose a device for in
situ lapping of valve seat of turbine valve which saves cost of
maintenance.
5) A still further object of the invention is to propose a device for in
situ lapping of valve seat of turbine valve which prevents huge
production loss.
BRIEF DESCRIPTION OF THE DRAWINGS;
Fig. 1 shows a typical valve configuration in assembled condition.
Fig. 2 shows the assembly of the lapping tool device.
Fig 3 shows the plate having a central hole.
Fig 4 shows the alternate lapping ring made from a single plate with a
hole matching with stud (Item No. 3).
Fig 5 shows the lapping ring (1) of Fig 2 before being welded with the
plate (2) of Fig 3.

Fig 6 shows the lapping tool placed on the valve seat when fastened at
two places of the valve.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION;
An exemplary embodiment of the invention as depicted in accompanying
drawings will now be explained in details. However there can be several
other embodiments all of which are deemed covered by the specification.
The present invention relates to the correction of damaged valve seats
conforming to the required quality at the place of work with the help of a
lapping device (Fig 2.). This device of lapping is adopted to avoid sending
the valve from the work place back to the shop for repairing that usually
takes six weeks of time.
The lapping device consists of a lapping ring (1) of Fig 5 welded to a plate
(2) in fig 2 having a hole for fixing the stud (3). The other end of the stud
goes through a nut (4), washer (5) and a central hole of a channel (6). Nut
(4) is kept loose on the stud (3). Washer (5) is welded to the channel (6).
The flat washer (5) is placed in between the nut (4) and the channel (6).
Channel (6) has two holes (7) at the two ends, the distance of the two
holes (7) being exactly the same as the distance of the clamping holes on

the valve body (Fig 6) matching with two holes of the pitch circle diameter
of the holes on the body (Fig 6). The end of the stud goes through a
matching nut (9) which is welded to a handle (8). The handle (8) is made
from 25/30 mm rod. The stud has threaded length of about 100 mm at
both ends. The stud length is 1200 mm having specification M 30/36.
The lapping ring (1), the main part of the device used for correcting the
damaged surface of valve seat (Fig 1) is made of wear resistant hard
material with bottom ground smooth and its internal and outer diameter
being selected as per the dimension of the valve suitability. The lapping
ring (1) can also be made of a single plate (Fig 4) instead of fabricating
item 1 (Fig 5) and item 2 (Fig 3).
The application of this device is manually controlled where the operator
monitors the progress of the result while continuing the operation till the
satisfactory results achieved.
At the time of lapping the valve seat, the valve cone along with cover
assembly is removed when the valve seat to be lapped is exposed (Fig 6).
The area to be lapped is plain and straight.

The device is inserted inside the valve body. Proper alignment is made
and clamped on the valve with the help of clamping fasteners through
the holes (7). The lapping device in clamping position inside the valve
body is shown in Fig 6. Two matching nuts (10) are put, one at the top
and other at the bottom of the plate (2) through which the stud (3) goes
through. The two nuts (10) are tightened to make the lapping ring (1)
fixed with the stud (3). Nuts (10) are used for proper sitting of lapping
ring (1) on the damaged valve seat. One matching nut (4) on the stud (3)
is placed below the washer (5). Washer (5) is welded to the channel (6).
Then lapping paste is applied on the damaged valve seat before the start
of the operation. When the nut (4) is moved against the washer (5) the
lapping ring gets a feed towards the valve seat. After this a to and fro
motion is given to the lapping ring with the handle (8) to perform the
lapping operation. Then intermittent inspection, cleaning and application
of lapping paste is carried out and the lapping operation is continued
while the lapping pressure is delivered with the nut (4) till the desired
result is obtained. The device is dismantled and taken out. The valve seat
is then checked with actual component valve cone with colour contact. If
any discrepancy observed, relapping is done and the process continues
till the colour contact checking ensures a desired result.

WE CLAIM:
1. The lapping device for in situ lapping of valve seat of turbine valves
comprises ;
a lapping ring (1) welded to a plate (2) having a hole at the center to
fix the stud (3) having threads at both ends;
two nuts (10) placed at the top and bottom of the plate (2)
fixing the stud (3) with the lapping ring (1);
a channel (6) having two holes (7) at two ends for fixing with
valve body (Fig 6) and a central hole at the middle accommodating
the stud (3) which rotates inside the matching nut (4) characterized
in that the lapping ring is given feed towards the valve seat by
rotating the nut (4) against the washer (5);
a handle (8) fixed to a nut (9) and stud (3) characterized in that the
said lapping device being imparted a to and fro motion by the
handle (8) is capable of smooth lapping of valve seats.
2) The lapping device for in situ lapping of turbine valves as claimed
in claim 1, wherein the lapping ring is made of a wear resistant
hard material, the bottom of the ring being ground smooth.

3) The lapping device for in situ lapping of turbine valves as claimed
in claim 1, wherein the lapping being performed with lapping paste
applied on valve seat.
4) The lapping device for in situ lapping of turbine valves as claimed
in claim 1, wherein the lapping process intermittently checked by
colour contact and finally between valve seat and valve cone.

The lapping device for in situ lapping of valve seat of turbine valves
comprises ;
a lapping ring (1) welded to a plate (2) having a hole at the center to
fix the stud (3) having threads at both ends;
two nuts (10) placed at the top and bottom of the plate (2)
fixing the stud (3) with the lapping ring (1);
a channel (6) having two holes (7) at two ends for fixing with
valve body (Fig 6) and a central hole at the middle accommodating
the stud (3) which rotates inside the matching nut (4) characterized
in that the lapping ring is given feed towards the valve seat by
rotating the nut (4) against the washer (5);
a handle (8) fixed to a nut (9) and stud (3) characterized in that the
said lapping device being imparted a to and fro motion by the
handle (8) is capable of smooth lapping of valve seats.