Valve was developed using air bearings which provide frictionless operation. The servo valve is of the flat plate type with rectangular meter openings. Fluid bearings support the metering plate. The overlap is adjustable by means of a variable hinge block support

Dustin, M. O.

English

NASA Technical Reports Server

Control Port 
Metering Plate [1
h2 
iii 
h1
g Plate 
November 1968	 Brief 68-10440 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information-, Springfield, Virginia 22151. 
Low Friction Servo Valve 
Top 
Cover Removed	 Fluid Bearing Torque Motor
A2	 Body 
PA 1 
Hinge
Bottom 
A valve has been developed using air bearings which 
provide frictionless operation. The servo valve is of 
the flat plate type with rectangular meter openings. 
Fluid bearings support the metering plate. The over-
lap is adjustable by means of a variable hinge block 
support. In conventional valves, this can only be done 
in the original fabrication of the valve. 
The valve shown at the left above is a three-way 
plate valve positioned by an electrical torque motor. 
This valve consists of a metering means positioned by 
the torque motor to control the now of fluid between 
the supply port and control port or between the con-
trol port and exhaust port. This is done by varying the 
area of the opening created between the metering plate 
and body. The area of the opening is proportional to 
the electrical torque motor current. Although the
valve shown uses a torque motor for positioning the 
metering means, the servo valve is not restricted to this 
type of actuator. 
The metering plate is supported between the body 
and the cover by a hinge at one end and by the fluid 
bearings at the other. The action of the fluid bear-
ings is to keep the plate centered between the two 
halves of the body and to resist any external force 
which would tend to cause the plate to rub against the 
body causing friction in the valve action. Operation 
of the fluid bearings is illustrtted at the right above. 
This is a simplified sketch showing a metering plate 
supported between two halves of the body. The dis-
tance, b, is fixed by spacers (not shown). For clarity, 
only one fluid bearing on each side of the plate is 
shown. In an actual application, several would be used 
(continued ovenleol) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000439 2020-03-12T05:59:49+00:00Z
These Views 
Shown with 
er 
ved 
Underlap
Plate 
r 
Location of Air 
Pressure	 Decrease	 Bearings, on Both 
Plate	 Sides of Plate 
Positioned Increase	 Pressure 
By Torque	 11
n \ 
Motor
2-- L
	 1	 -.1
Hinge 
L 
Body	 a) Zero Lap	 Cover	 b) Overlap 
(L	 a!8 
co	 C	 C1 
OU) 
UJ
on each side of the plate. The fluid is supplied to the 
bearings at a constant pressure, P. Two restrictions 
are creatd, a fixed resistance at the drilled hole d, and 
a distributed resistance from the drilled hole out to the 
edge of the plate. The distributed resistance decreases 
as the clearance, h, increases. This causes a, decrease 
in the average pressure, a• If a force is applied up-
ward to the plate, the clearance, h 2, will decrease, 
causing the average pressure, P, to increase. Also, 
the clearance, h 1 , will increase causing the average 
pressure, pal' to decrease. The result is a net pressure 
differential across the plate in a direction opposing the 
applied force. 
The other unique feature of the servo valve is the 
adjustment for changing the overlap of the valve. The 
operation of this feature is shown in the above fig-
ure. By loosening the two screws, L, which hold the 
hinge support block, M, to the body; the support 
block may be moved up or down. Because of the angle 
of the metering edges, the overlap will decrease when
the block is moved up and increase when the block is 
moved down. Figure c shows the block moved to the 
extreme upward position resulting in an underlapped 
condition. 
Notes: 
I. The servovalve can be used in closed loop pres-
sure control systems that require large instantan-
eous now rates at low pressures. It has been used 
with a supply pressure up to 30 psig. 
2. No additional documentation is available for this 
innovation. 
3. Technical questions concerning this innovation 
may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B68-10440 
Patent status: 
No patent action contemplated by NASA. 
Source: Miles 0. Dustin 
(LEW- 10574) 
Brief 68-10440	 .	 Category 05


Low friction servo valve

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