MTS Series 244 Actuators - Manual (Page 16)

Series 244 Hydraulic Actuator Major Components
Description Component Item
The piston rod has a hardened steel insert that provides an
internal thread for mounting load cells, swivels, and interface Piston rod end 1
fixtures. The Model 244.51 Actuator has no insert; internal
threads are machined directly into the piston rod end.
The high-capacity nonmetallic bearings bond directly to the
end caps. The non-metallic bearings are standard because of Bearing 2
their high side-load tolerance and resistance to failure from
galling and seizure.
The cushions protect the actuator from the effects of
high-speed and high-mass forces. They prevent the actuator Cushion 3
from contacting the end caps. The Model 244.41 and 244.51
Actuators do not have hydraulic cushions.
High-pressure hydraulic fluid enters the cylinder through one
of these control ports. As pressure is applied to one port, the Extension Port/
Retraction Port 4
other port is opened to a return line causing the actuator to
extend or to retract. Fluid flow through these ports is controlled
by the servovalve.
A reinforced Teflon seal (if equipped) on the piston provides
a positive seal and reduces friction. Grooves on the piston Piston seal 5
lubricate the piston surface during short-stroke, side-loaded
tests. For high-speed cyclic testing applications, the piston
seal can be omitted. The close tolerance fit provides an
effective viscous seal.
The Series 244 Actuator is equipped with a double-ended
piston rod. The double-ended piston has equal areas on both Piston rod 6
sides for balanced performance. It is machined from a single
piece of heat-treated alloy steel and is hard-chrome plated.
The piston rod is hollow to allow for installation and accurate
alignment of a displacement transducer.
The drainback port allows fluid that manages to leak past the
seals to be routed out of the actuator which prevents pressure
pockets from interfering with actuator performance. Drainback Port 7
The piston rod seals consist of a high-pressure seal and a
low-pressure/wiper seal in both the front end cap and the rear
end cap. High/Low Pressure
Seals 8
Model 244.1x and 244.2x Actuators [with force ratings under
100 kN (22 kip)], that are used in load frame/unit applications
do not contain high-pressure piston rod seals.
The high-pressure seal is designed for long life, low friction,
and exceptional performance in high-frequency,
low-displacement applications. A small amount of hydraulic
fluid is allowed to flow past the high-pressure seal for
continuous bearing lubrication. Drainback ports return the
16 Series 244 Actuators Product Information
Introduction