FIELD OF INVENTION
The present invention relates to a arrangement of valves and cams newly
designed and manufactured for improving the valve lift for regulation of steam flow to
HP cylinder of 200/210 MW steam turbine. More particularly, the invention relates to
the improvement of opening of each control valve depending on the valve lift that
governs the amount of steam flow to the cylinder.
BACKGROUND OF THE INVENTION
Control Valves are mounted on the HP Casing of Steam Turbine to
regulate the Steam Flow to the HP Turbine. The % opening of each Control Valve which
is stated in terms of valve lift, governs the amount of steam flow to the HP cylinder.
The opening of all the four valves is controlled by a single Control Valve Servomotor
(CVSM). The spindles of the control valves are connected to a camshaft by their
respective levers. This camshaft has a gear mounted at one end. A rack arm is
connected to the CVSM, the other end of which rests on the gear of the camshaft.
Hence, as soon as the CVSM moves upwards or downwards, this motion is transmitted
via the rack arm to the gear of camshaft which in turn rotates the camshaft. Four cams
are mounted on the camshaft to control the lift of four control valves. The contour of
the Cams and their relative positioning with respect to each other and to the CVSM
position, defines the sequence of opening of Control Valves and the Valve Lift for a
particular CVSM position. Cams have been designed and suitable sequence of valve
opening has been designed keeping in view the valve lift required to be maintained with
respect to the Camshaft rotation and Control valve Servomotor motion. The present

invention was successfully installed at Obra-9 site and is functioning satisfactorily since
then.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a arrangement of
valves and cams newly designed and manufactured for improving the valve lift for
regulation of steam flow to HP cylinder of 200/210 MW steam turbine which is capable
of improving the opening of control valve to govern the amount of steam flow to the HP
cylinder of the turbine.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 - Shows the arrangement of valves and cams
Fig. 2 - Shows the relative position of cam on camshaft
Fig. 3 - Shows cam for valve no. 2
Fig. 4 - Shows cam for valve no. 3
Fig. 5 - Shows cam for valve no. 4
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The invention relates to an arrangement of valves (11, 12, 13, 14) and
cams (6, 7, 8, 9) for controlling the valve number 1, 2, 3, 4 of HP cylinder of a 200/210
MW Steam turbine for regulation of steam flow through the turbine. Cams (7, 8, 9) are
designed and manufactured with suitable contour to achieve the required valve lift for
governing the steam flow. A new cam arrangement to obtain the correct sequence of
opening of valves and their angle of opening relative to each other is arranged when
valve no. 2 (12) and valve no. 4 (14) (Refer Fig. 1) are interchanged. There are two
levers to transmit the roller movement to the valve spindle in case of side mounted

valves and a single lever to transmit the roller movement to the valve spindle in case of
top mounted valves. Earlier position of Valve No. 2 (12) i.e. Top mounted is now
interchanged with side mounted Valve No. 4 (14). Hence, the new arrangement and
new cams with suitable contour have been designed for effective steam regulation in
this changed scenario.
Valve lift is calculated based on the roller lift and lever ratio to form the basis for
valve lifts at different intervals of Camshaft rotation when simulation is done to get the
points of trajectory of the roller over the cam with an interval of 5° of Camshaft rotation
and to obtain the complete contour of Cam for the required valve lift.
Control Valves are mounted on the HP Casing of Steam Turbine (refer Fig. 1) to
regulate the Steam Flow to the HP cylinder (10). The % opening of each Control Valve
which is stated in terms of valve lift, governs the amount of steam flow to the HP
cylinder. The opening of all the four valves is controlled by a single Control Valve
Servomotor (CVSM) (1). The spindles of the control valves are connected to a camshaft
(2) by their respective levers (3). This camshaft (2) has a gear (4) mounted at one end.
A rack arm (5) is connected to the CVSM, the other end of which rests on the gear (4)
of the camshaft (2). Hence, as soon as the CVSM moves upwards or downwards, these
motions are transmitted vide the rack arm (5) to the gear (4) of camshaft (2) which in
turn rotates the camshaft. Four cams (6, 7, 8, 9) are mounted on the camshaft (2) to
control the lift of four control valves (11, 12, 13, 14). The contour of the Cams (6, 7, 8,
9) and their relative positioning with respect to each other and to the CVSM (1)
position, defines the sequence of opening of Control Valves and the Valve Lift for a
particular CVSM position.
Earlier, Valve No. 2 which also has a relief valve could not be opened
beyond a lift of 24mm as the numbers of nozzles placed in front of the valve were 5
which were not enough to support the steam flow for a valve opening of 37mm. On the
contrary, the no. of nozzles in front of valve no. 4 was 11 for the required opening of
only 14mm.

The reduction in lift of valve no. 2 (12) because of the aforesaid reasons
was contributing to the overloading of CVSM (1) while opening of valve no. 3 (13)
which had a steep rate of valve lift to compensate for the low lift of valve no. 2 (12).
This was a major contributing factor for the high level of hunting observed and reported
from site repeatedly. Hence a new arrangement of valves had to be devised and new
cams had to be designed for the new arrangement to get the desired valve lift
characteristics. In order to achieve the above, valve no. 2 & 4 (12, 14) were
interchanged while retaining their column & lever assembly at their original position so
that the distance between the camshaft & hinge and camshaft center & roller center
remains unaltered. After the above-referred change valve no. 2 now faces 11 nozzles so
that a valve lift of 37 mm can be managed. The next stage was the sequence of
opening of valves and their angle of opening relative to each other. A new cam
arrangement was designed to achieve the desired characteristics (Refer Fig-2). Thirdly,
new cams were designed for the first time keeping in view the new arrangement of
valves and the desired valve lift. The cams were designed by using kinematic inversion
since the assembly connecting the roller to the valve spindle was complicated in nature.
In the earlier existing arrangement for valve no. 2 (12), the roller was attached to one
end of the lever which was hinged at the other end and the spindle movement was
transmitted by the use of a roller pin placed inside groove made in the lever (Refer Fig-
1) while in the new arrangement two levers were used to transmit the roller movement
to the valve spindle (Refer Fig-1). The lever ratios of both the arrangements were
calculated and based on that lift of roller was calculated from the desired value of valve
lift. Now, cams (7, 8, 9) with suitable contour were designed and manufactured to
achieve the desired roller lift. It is at this stage that the kinematic inversion was used to
get the contour of the cam for each valve wherein cams were kept stationary and roller
along with the lever was rotated about the hinge for suitable interval of angles in a 2-D
simulation and contour points were hence obtained. Based on the roller lift valve lift
was calculated using lever ratio. The lever ratio was calculated using the arm length
and angle rotated about the hinge wherein displacement of one end of lever was used

to obtain the displacement of adjoining end of connecting lever and finally the valve
spindle connected to the lever. This forms the basis for valve lifts at different intervals
of camshaft rotation. To the scale line diagram of complete assembly including Cam,
Roller and Levers was drawn and simulations were done to get the points of trajectory
of the roller over the Cams with an interval of 5° of camshaft rotation. Base circle radius
for cams was taken as 87.5mm and location of the key-way slot on cams was selected
to ensure the opening of valve at a predetermined angle of camshaft rotation as per the
sequence of opening of valves. Thereafter contour points were obtained by
aforementioned simulation. Finally the contour points were joined using suitable curves
and straight portions to get a smooth contour. The final design of Cams was thus
arrived at and detailed to the scale drawings were finalized and released for
manufacturing. Cams were machined out of Carbon Steel Forgings which is a suitable
material for the required application.
Final detailed drawings for Cam (7) for valve no. 2(12), Cam (8) for Valve
No. 3(13), Cam (9) for valve no. 4 (14) are shown in Fig. 3, Fig. 4, Fig. 5 respectively.
Cams were installed at site successfully and gave the desired reading of
characteristics i.e. valve lift. The whole arrangement is functioning satisfactorily at Bhel
site since then.

WE CLAIM
1. Arrangement of valves and cams newly designed and manufactured for
improving the valve lift for regulation of steam flow to HP cylinder of 200/210
MW steam turbine, the said arrangement comprising;
designing and manufacturing the cams (7, 8, 9) with suitable contour to achieve
the required roller lift;
interchanging valve No. 2 (12) and valve no. 4(14) retaining their column and
lever assembly at their original position keeping the distance between the
camshafts and hinge and camshaft center and roller center unaltered;
introducing a new cam arrangement to obtain the correct sequence of opening
of valves and their angle of opening relative to each other;
implementing two levers to transmit the roller movement to the valve spindle;
wherein the valve lift is calculated based on the roller lift and lever ratio to form
the basis for valve lifts at different intervals of camshaft rotation when simulation
is done to get the points of trajectory of the roller over the cam with an interval
of 5° of camshaft rotation and to obtain the complete contour of cam for the
referred lift.
2. The arrangement as claimed in claim 1, wherein the opening of all the four valves
(11, 12,13, 14) is controlled by a single control valve servomotor (CVSM) (1).

ABSTRACT

The invention relates to an arrangement of valves and cams for controlling the valve number 2, 3, 4 of HP cylinder of a 200/210 MW Steam turbine for regulation of steam flow through the turbine. Cams (7, 8, 9) are designed and
manufactured with suitable contour to achieve the required valve lift for governing the steam flow. A new cam arrangement to obtain the correct sequence of opening of valves and their angle of opening relative to each other, is arranged when valve no. 2(12) and valve no. 4(14) are interchanged. Two levers to transmit the roller movement to the valve spindle is implemented. Valve lift is calculated based on the roller lift and lever ratio to form the basis for valve lifts at different intervals of Camshaft rotation when simulation is done to get the points of trajectory of the roller over the cam with an interval of 5° of Camshaft rotation and to obtain the complete contour of Cam for
the referred lift.