Valve actuators

An actuator for a valve in which valve opening and closing is effected via a rectilinearly movable member having, at one end, a driving device and, at its other end, a return-movement arrangement. To-and fro movement of the member under the control of the driving device and return-movement arrangement opens or closes the valve, or vice versa. The return-movement arrangement includes a ramp connected to the member and a resilient energy storing cushion for acting oppositely to the driving device on the member with a bridging roller transmission rolling contacting the ramp so that, depending on direction of movement of the member, energy is either stored in or dissipated from the cushion.

The invention relates to an actuator which may be remotely controlled by 
mechanical, hydraulic or pneumatic means and returns to its initial 
position when it is no longer acted upon, providing the process with which 
it is associated with a pressure and return torque whose modulus varies 
along the travel depending on the operating principle and law of said 
process. 
It relates more particularly to an actuator using a hydraulic or pneumatic 
single-acting ram designed for the operation of butterfly valves or the 
like and which comprises a mechanical device storing energy for the return 
of the butterfly member and maintaining it in its extreme position when 
the driving pressure (hydraulic or pneumatic) is less than a certain 
value. 
It is known that actuators of this type must be able to define a very 
precise closed position, thus determining the seal of the valve and good 
behaviour of the seat or flexible ring. 
They must also be able to transmit to the control shaft of the butterfly 
member, the necessary torque, with the exclusion of any other force, to 
provide considerable torque at the time of closing of the valve, to ensure 
mechanical locking in the closed position and finally, to move the 
butterfly member as slowly as possible at the time of closing as well as 
opening, this being in order to make the decrease in the rate of flow 
regular and to prevent disturbances due to water-hammering at the time of 
closure. 
It is obvious that such characteristics may be obtained in one direction by 
means of a single-acting hydraulic or pneumatic ram associated with an 
appropriate transmission and conversion system (rectilinear 
movement/rotary movement). 
On the other hand, it is quite different for operation in the opposite 
direction of the actuator, in the absence of pneumatic or hydraulic 
pressure. 
In order to facilitate a return to the initial position of the ram and 
consequently of the valve when said ram is no longer acted upon by a 
pressure, storage systems have already been produced, comprising springs, 
for example simple helical springs, which are compressed by the rod of the 
ram when the latter is subject to a hydraulic control pressure, thus 
absorbing, in the form of potential energy, part of the energy of the ram 
and which restore this energy by pushing the rod of the ram back into the 
initial position, when the latter is no longer moving. 
Nevertheless, the use of such return springs does not make it possible to 
achieve the afore-mentioned properties and this is mainly due to the fact 
that the transmission and conversion system generally takes into account 
the fact that the pressure exerted by the rod of the ram is constant 
throughout its movement. 
Consequently, this system is no longer suitable, when, in the absence of 
control pressure, the actuator returns to its initial position under the 
effect of the springs which store energy. In fact, it is known that the 
force exerted by a spring is not constant, but varies depending on its 
extension. Consequently, if the action of the ram is intended to ensure 
opening of the valve, the force exerted by the return spring to ensure the 
closure of the valve will be greater at the beginning of the closing 
movement than at the time of closure, which is contrary to the objectives. 
The object of the invention is to eliminate these drawbacks. It proposes an 
actuator provided with an energy storage system which is compatible with 
the transmission and conversion system associated with the rod of the 
pneumatic or hydraulic ram, in order to obtain, during the return of the 
actuator to the initial position, in the absence of control pressure, a 
return force whose value varies depending on the movement of the rod of 
the ram according to a law appropriate to the objectives. 
Consequently, the actuator according to the invention is composed 
essentially of a driving member, for example a single-acting hydraulic or 
pneumatic ram, whereof the movable output member having a rectilinear 
movement (for example the rod of the ram) is integral with a mechanical 
transmission and conversion system (rectilinear movement/rotary movement) 
and at its end comprises at least one ramp on which bears and rolls at 
least one roller subject to the action of a resilient device serving as an 
energy store such that on the one hand, when the movable output member 
moves in one direction under the action of a control pressure emanating 
from the driving member, said ramp pushes the roller against the action of 
the resilient forces, a movement during which the resilient device stores 
part of the energy provided by the driving member in the form of potential 
energy and, on the other hand, in the absence of a control pressure of the 
driving member, such that this stored potential energy causes the return 
to the initial position of said output member by action of the roller on 
said ramp according to a law of variation of force/displacement, depending 
on the profile of said ramp, this profile consequently being adapted to 
the type of said transmission and conversion system and due to this, to 
the final objectives. 
According to one method of application of the actuator according to the 
invention to a butterfly valve whose opening and closure are obtained 
respectively by a rotation through a quarter of a revolution of the shaft 
of the butterfly member, the mechanical system for transmission and 
rectilinear movement/rotary movement conversion may comprise a connecting 
rod pivoted firstly to a sheave integral with the output member of the 
actuator and secondly to the end of a lever arm integral with a mandrel 
fixed on the drive shaft or square of the butterfly member. 
This transmission and conversion system advantageously makes it possible to 
obtain a driving torque on the drive shaft of the butterfly member, which 
torque, starting from the open position of the valve, increases 
progressively to the closed position in which it is theoretically infinite 
and this is for a substantially constant force of the driving member.

With reference to FIGS. 1, 2 and 5, the actuator 1, comprises a 
single-acting pneumatic ram 2 comprising, in conventional manner a 
cylinder 3 and piston 4 integral with a rod 5 moving in a rectilinear 
manner. In its central part, this rod 5 comprises a hub 6, to which is 
pivoted a connecting rod 7 in turn pivoted on a lever arm 8 integral with 
a mandrel 9 fixed to the actuating shaft 10 of a butterfly valve. In this 
respect, it should be noted that the rod 5 of the ram 2, as well as the 
parts of the transmission and conversion system, namely the connecting rod 
7 and lever arm 8, are located in planes at right-angles to the drive 
shaft of the butterfly member of said valve. 
At its free end, the rod 5 of the ram 2 supports a ramp or pointed cam 12 
whereof the end slides in a guiding tube 13 serving to ensure a purely 
rectilinear movement without any lateral clearance, for said rod 5. 
Bearing against the outer surface of the pointed cam 12 are a plurality of 
rollers 14, which make it possible to transfer to said cam 12, by means of 
an angular return system, the pressure exerted by a resilient member 
arranged coaxially to the outer periphery of said guiding tube 13. 
In the example illustrated, the return system is composed of a movable 
member or rocker 15, in the shape of a portion of a ring, having an angle 
at the centre approximately equal to 90.degree., whereof the outer 
peripheral surface bears on the inner peripheral surface, of complementary 
shape, of an abutment member 16 integral with the body 17 of the actuator 
1. To limit the loss of energy due to friction between the movable member 
or rocker 15 and the abutment member 16, as much as possible, a needle 
bearing or roller bearing device 18 is disposed between the two said 
surfaces. 
At one end, the movable member 15 supports a pivotally mounted roller 14, 
which comes into contact with the pointed cam 12 and, on the other side, a 
roller 19 against which bears a washer 20 sliding on the guide tube 13 and 
subject to the force of the resilient member. Thus, during movements of 
the movable member 15, the roller 19 may roll radially on the washer 20. 
Similarly, the resilient member is constituted by a pile of resilient 
washers 22 arranged around the guidance tube 13 between a part 23 of the 
body 17 of the actuator, serving as an abutment and said washer 20. 
Thus, in the case where closure of the valve is obtained by action of the 
resilient member, in the closed position of the valve (FIG. 1), the rod 5 
is "lowered" and the rollers 14 come into contact with the small diameter 
end of the pointed cam 12. The resilient member is thus partly slackened. 
To obtain opening of the valve, the ram 2 is pressurised in order to cause 
the movement of the rod 5. During this movement, the pointed cam 12 pushes 
back the rollers 14, which, by means of the return system, causes the 
compression of the resilient member. Thus, part of the energy provided by 
the ram 2 is stored, in the form of potential energy, by the resilient 
member. At the end of the opening movement, the rollers 14 are in contact 
with the large diameter of the cam (FIG. 2). 
When the pressure inside the ram 2 is eliminated, the rod 5, which is 
subject only to said return force, moves in the opposite direction to 
previously, causing closure of the valve (FIG. 1). 
During this displacement, the return force follows a law of variation 
depending directly, on the one hand, on the nature of the resilient member 
and, on the other hand, on the profile of the cam 12. Naturally, this law 
of variation which is transformed by the transfer function of the 
transmission and conversion system, is established in order to fulfill the 
opening and closing laws of the valve in an optimum manner. 
Referring to FIGS. 3 and 4, the actuator, which has a symmetrical 
arrangement of the transmission and conversion system 27, ensures that the 
valve returns to the open position, by the energy storing system 28, 
whereas the closure of the valve is ensured by the action of the ram 26. 
In order to facilitate the opening operation in the case where the valve is 
in the closed position, under the effect of the resilient device (or vice 
versa) when hydraulic or pneumatic energy is not available, for example in 
the case of a breakdown of the installation providing or distributing the 
energy or when starting up the installation, the invention provides an 
emergency control system. 
To this end, a tapped opening 29 coaxial to the rod 5 of the ram and 
located at the rear of the pointed cam 12 is provided in the body of the 
actuator. 
This opening 29 is normally closed by a stopper 31, which may be removed 
and replaced when necessary, when the hydraulic or pneumatic energy fails, 
by a screwthreaded rod 32 which is screwed into the opening 29 and during 
screwing pushes back the rear of the pointed cam 12, thus replacing the 
force of the hydraulic or pneumatic pressure which is not available. 
FIGS. 6, 7 and 8 make it easier to illustrate the operating principle of 
the transmission and conversion system used in the actuator shown in FIGS. 
1, 2, 3 and 4, and in particular the respective positions assumed by the 
hub 6, the connecting rod 7 and the mandrel 9 in the opening position 
(FIG. 6), in the intermediate position (FIG. 7) and in the closed position 
(FIG. 8) of the valve. 
It thus appears that if the hub 6 to which the connecting rod 7 is pivoted, 
is subject to a constant force, in the opening position shown in FIG. 6, 
the torque available on the axis of the mandrel satisfies the equation c = 
F.h (h being the distance of the connecting rod 7 from the axis of the 
mandrel 9). 
During the movement of the hub 6, one firstly notes a slight decrease in 
the torque C with a slight reduction of the distance h.sub.2 (FIG. 7) 
which is then compensated for by the increase of the component F.sub.2 of 
the force F on the longitudinal axis of the connecting rod 7, this torque 
then increasing progressively on reaching the closed position illustrated 
in FIG. 8 where it is theoretically infinite. 
The slight decrease in torque in the intermediate position is easily 
compensated for by an appropriate structure of the profile of the pointed 
ramp 12.