4 | GE Oil & Gas
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Description
The
Masoneilan
37/38
spring-diaphragm
actuator is a simple, powerful, mechanical device.
There are two general types:
Air-to-Extend Stem
and
Air-to-Retract Stem
. Actuators are designated
by case size: Nos. 9, 11, 13, 15, 18 and 18L.
The nominal range of a spring-diaphragm
actuator is the air pressure range in pounds per
square inch (psi) for rated stroke under no load.
Common ranges are 3–15 psi and 6–30 psi. The
spring range and maximum allowable supply
pressure are marked on the serial plate. For a 3–
15 psi nominal range, the stem will start to stroke
when the air pressure reaches 3 psi, and will
complete the stroke when the pressure reaches
15 psi (plus or minus 5%).
In the air-to-extend actuator, conformation of the
molded diaphragm to the diaphragm plate serves
as a flexible upper guide for the actuator stem
(26). The lower guide is an oil-impregnated bronze
bushing (37) located in the spring adjustor (36).
The air-to-retract actuator differs from the air-to-
extend unit in that the spring (22), spring barrel
(71) and spring adjustor (36) are located
above
the
diaphragm plate (40) and diaphragm (39) which
are inverted. A gasket (19) at the joint of the
diaphragm case and yoke and a packing box
around the actuator stem prevents air leakage.
The diaphragm acts as a flexible upper guide and
the packing box assembly as the lower guide for
the actuator stem.
Air connections are 1/4" NPT. Connections are
located in the upper diaphragm case (air-to-
extend actuators) or yoke (air-to-retract actuators).
Standard
Actuator Size
Effective
Diaphragm
Area (sq. in.)
Maximum
Stroke (in.)
9
45
¾
11
71
1
13
105
1 ½
15
145
2
18
200
2 ½
18L
200
4
Life Period
The current estimated useful life period for the
Masoneilan 37/38 actuator is 25+ years. To
maximize the useful life of the product it is
essential to conduct annual inspections, routine
maintenance and ensure proper installation to
avoid any unintended stresses on the product. The
specific operating conditions and environmental
conditions will also impact the useful life of the
product. Consult the factory for guidance on
specific applications if required prior to installation.
Maintenance
Air-to-Extend Actuators (Type 37)
Diaphragm Replacement
Before disassembling the actuator, all spring
compression should be relieved by turning the spring
adjustor (36), to prevent the upper case popping up
when the cap screws (45) are removed. This is
especially important on actuators with a high initial
spring setting. Remove cap screws (45), nuts (46) and
upper diaphragm case (43). Remove nut (30) and
washer (41) to release the diaphragm (39). If possible,
the replacement diaphragm should be of the molded
type supplied by GE Masoneilan, but in an
emergency a diaphragm may be cut from flat sheet
stock for up to and including No. 15 actuators. To
allow sufficient stroke without restriction due to
flatness of the diaphragm, the diaphragm bolt circle
should be about 10% greater than that of the
diaphragm case.
Replace washer (41), nut (30) and upper diaphragm
case.
Spring Adjustment
An air supply, with a gauge and regulator, should be
piped to the upper diaphragm case for this
adjustment. Adjust spring compression so that the
actuator stem (26) just begins to move when air
pressure reaches minimum pressure of the range
stamped on the serial plate. This movement is most
easily detected by feeling the stem as air pressure is
applied.
Note:
Adjust spring compression only when there is
no air pressure on diaphragm.
