Making a Reliable Actuator Faster
and More Affordable
Industrial Productivity/Manufacturing Technology
Originating Technology/ NASA Contribution
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Stennis Space
Center is NASA’s lead center for rocket propulsion
testing and manages the Agency’s rocket propulsion
test programs and facilities for current and
future space vehicles. |
Before any rocket is allowed to fly and be used for a
manned mission, it is first test-fired on a static test
stand to verify its flight readiness. NASA’s Stennis
Space Center provides testing of Space Shuttle Main Engines,
rocket propulsion systems, and related components with
several test facilities. It has been NASA’s test-launch
site
since 1961.
The testing stations age with time and repeated use;
and with aging comes maintenance; and with maintenance
comes expense. NASA has been seeking ways
to lower the cost of maintaining the stations, and has
aided in the development of an improved reliable linear
actuator that arrives onsite quickly and costs less money
than other actuators.
In general terms, a linear actuator is a servomechanism
that supplies a measured amount of energy for the operation
of another mechanical system. Accuracy, reliability,
and speed of the actuator are critical to performance
of the entire system, and these actuators are critical
components of the engine test stands.
Partnership
An actuator was developed as part of a Dual-Use Cooperative
Agreement between BAFCO,
Inc., of Warminister, Pennsylvania,
and Stennis.
BAFCO identified four suppliers that manufactured
actuator components that met the rigorous testing standards
imposed by the Space Agency and then modified these components
for application on the rocket
test stands.
In partnership with BAFCO, the existing commercial products’
size and weight were reworked, reducing cost and delivery
time. Previously, these parts would cost between $20,000
and $22,000, but with the new process, they now run between
$11,000 and $13,000, a substantial savings, considering
NASA has already purchased over 120 of the units. Delivery
time of the cost-saving actuators has also been cut from
over 20 to 22 weeks to within 8 to 10 weeks.
The redesigned actuator is commercially available, and
the company is successfully supplying them to customers
other than NASA.
Product Outcome
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The high-pressure
gaseous oxygen panel which feeds the ignition
system for a rocket engine combustion device,
located at ground level on the E-I Test Facility,
Cell 3. The valve identified as PCV-10A2892-GO
is operated by means of the high-performance
actuator developed as a part of the Dual-Use
Cooperative Agreement with BAFCO, Inc. |
The BAFCO Model 773 is a next-generation, high-thrust,
high-response actuator designed to meet performance
standards in aerospace, industrial, and petrochemical
applications. It meets the National Fluid Power Association
standards for cylinder performance, as well as meeting
U.S. and European standards for electrical component
functions.
The actuators are adaptable for use in a variety of industrial
applications, including steam turbines, process-control
valves, dampers, for motion control, and a variety of
other mechanical purposes. Customers are taking advantage
of them, since the time and cost of manufacturing are
less than those of the other, less-reliable actuators.
Previously used linear actuators worked inconsistently
as positioning devices, and their ability to decelerate
to gentle stops ranged from unsatisfactory to nonexistent.
The BAFCO 773 offers solutions to both of these problems
and more.
To solve the problem of positioning reliability, the
flow of hydraulic fluid to the two ports of the actuator
cylinder is controlled by a servo valve that is controlled
by a signal from a servo amplifier that, in turn, receives
an analog position-command signal from a supervisory
control system of the facility. As the position command
changes, the servo valve shifts, causing a greater flow
of hydraulic fluid to one side of the cylinder, thereby
causing the actuator piston to move to extend or retract
a piston rod from the actuator body. A linear variable
differential transformer (LVDT), directly linked to the
piston, provides a position-feedback signal, which is
compared with the position-command signal in the servo
amplifier. When the position-feedback and position-command
signals match, the servo valve moves to its null position,
in which it holds the actuator piston at a steady position.
The actuator also includes a deceleration feature for
both extremes of the piston stroke. When the actuator
is used to open and close a valve, the deceleration feature
prevents damage to valve seats and other components during
cycles of rapid stroking. Because the resolution of the
LVDT is, for practical purposes, unlimited, the position
feedback from the LVDT acts, in conjunction with the
deceleration feature, to afford maximum protection against
damage in those ranges of position in which protection
is most needed.
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The BAFCO Model
793 linear actuator, one of the newer models
in the family of products created in the Dual-Use
Cooperative Agreement. |
In addition to answering the previous two problems, the
improved actuators help to eliminate leaks associated
with common tubing problems by having the components
within the actuator connected to a high-pressure hydraulic
fluid via a manifold.
The Model 773 has been so successful that BAFCO applied
the same concept of off-the-shelf parts modified for
specific applications to the development of the Model
775 and 793 as well. The Model 775 rotary actuator was
designed as a cost-competitive alternative to pneumatic
or electric actuators and operates
90-degree rotation valves of dampers in modulating,
on-off and fail-safe applications. Industries that will
benefit from this technology include aerospace, petrochemical,
well-choke services, power generation, and manufacturing.
The Model 793 linear actuator was designed to extend
the existing line of 773 actuators for use with very
small linear valves. This new short-stroke actuator featuring
auxiliary components common to the Model 773 actuators
provides BAFCO the ability to supply actuators to a much
larger range of valve sizes.
BAFCO Models 773, 775, and 793 actuators have demonstrated
improved accuracy and precision, increased operating
speeds, and extended life expectancy over
the pneumatic and electric actuators previously used
industry-wide. Domestically, BAFCO has made sales to
several NASA facilities, Honeywell, the University of
Purdue, several U.S. Air Force facilities, and other
major suppliers of the aerospace industries. Internationally,
BAFCO has sold Model 773 actuators to an oil refinery
in Serbia and Model 775 actuators to several oil refineries
in China. To date, sales of BAFCO’s 773, 775, and 793
lines of actuators, including sales to NASA, total more
than $2 million, with no foreseeable end to the market
potential.
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