PNEUMATIC PRESSURE TRANSMITTER

COMMUNICATEUR DE PRESSION PNEUMATIQUE

English Abstract

PNEUMATIC PRESSURE TRANSMITTER
Abstract
A pneumatic pressure transmitter for converting electrical
signals into pressure, comprising a lever, an auxilliary
spring, two separate pilots for inlet and exaust valves, a
loading spring and a stepped motor inside the knob. The
pneumatic pressure transmitter can work in the manual or
automatic modes. The same regulating mechanism can be used
for control valve positioners, pressure regulators, pneumatic
relays and others.

Claims

THE EMBODIMENT OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE ARE DEFINED AS FOLLOWS:
1. A pneumatic pressure transmitter comprising:
a frame with a control pressure chamber, a loading
spring chamber and a diaphragm which separates said chambers:
an exhaust valve mounted in the centre of said diaphragm;
an inlet valve;
an inlet pilot (2) and an exhaust pilot (10) means for
closing said inlet and exhaust valves;
a lever with a pivot fixed at the frame;
an auxilliary spring and
a loading spring means for putting a reference pressure
on the diaphragm;
said inlet and exhaust pilots, lever and auxilliary spring are
housed inside the control pressure chamber and interact in
such a way that the auxilliary spring pushes the exhaust pilot
and one arm of the lever while the other arm of said lever
pushes the inlet pilot with a force sufficient to keep the
inlet and exhaust valves closed when the pressure in the
control pressure chamber is counterbalanced by the force of
the loading spring: whereby a surplus pressure in the control
pressure chamber moves the diaphragm and opens the exhaust
valve; lack of pressure in said chamber moves the diaphragm
under a force of the loading spring in the opposite direction,
pushes the exhaust pilot, compresses the auxilliary spring
and opens the inlet valve.
2. A pneumatic pressure transmitter as defined in claim 1
further comprising:
a threaded shaft and a sliding nut means for compressing
the loading spring by rotating said threaded shaft;
-3-

a stator of the stepped motor fixed at the frame
a rotor of the stepped motor mounted outside the stator
and rigidly fixed with the knob and the threaded shaft means
for rotating said shaft;
whereby the treaded shaft can by rotated manually by the knob
or electrically by the stepped motor.
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Description

Specification
1. This invention pertains to the field of instrumentation
and in particular for use with pneumatically powered control
valves. Presently available transmitters (transducers) are
complicated and expensive. Simple regulators cannot be used
because of the big force that is necessary to operate them
znd structurally complicated alterations must be made.
The object of the present invention ;s to alleviate the
problems mentioned above by providing a new regulating mecha-
nism which closes the inlet valve agaist the flow and uses
the auxilliary spring to compensate the force of supply pres-
sure. The pneumatic pressure transmitter has a fast response,
a small "dead zone", a small hysteresis and low air consumption.
It is simple to manufacture and service. The low force neces-
sary to operate the pneumatic pressure transmitter allows
for the installation of a stepped motor and for the use of
the pneumatic pressure transmitter in a manual or automated
control.
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1 ~8940
2. In ths drawings which illustrate embodiment of the
invention t
Fig, 1 is an elevation showing the pneumatic pressure
transmitter,
Fig. 2 is a crosY section taken along the line I-I
of the Fi~, 1,
3. As it is illustrated in the drawing, a frame of the
pneumatic pressure transmitter 6, 13, 21 (See Fig, 1) forms
a control pressure chamber 15 and a loading spring chamber 25,
separated by a diaphragm 26 with an exhaust valve 9 in the
centre, The fluid flows through an inlet connector 7 and
an inlet valve 1 into the control pressure chamber and to an
outlet connector 14, The control pressure chamber houses a
regulating mechanism, comprising an inlet pilot 2, an exhaust
pilot`lO, a lever 8 with a pivot 5 fixed at the frame and
an auxilliary spring 12. Guides 3, 4, 11 and 26 provide a
travel cantrol for the pilots.~ The pilots, the lever and the
auxilliary sprin~ interact in such a way that the auxilliary
spring pushes the exaust pilot and one arm of the lever, while
the other arm of` the lever pushes the inlet pllot. The auxil-
liary spring has to be sufficiently strong to keep both valves
clo~ed when the control pressure is counterbalan~ed by the
force of the loading spring, Surplus or lack of pressure
moves the diaphragm and opens the exhaust or inlet valve,
To compress the loading spring a threaded shaft 22 and a
sliding nut are used. Such a combination with a bearing 17
prevents the threaded shaft from axial mo~ement.
A stator of the variable reluctance type stepped motor 18
with windings 16 is fixed at the frame. A rotor 2 is rigi~ly
connected with a knob 19 to the threaded shaft 22 and can be
turned manually or electrically to change the control pressure.