STI RTQ Series, Instruction Manual, Page: 31 / 44

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Manual 5300, rev. 09 06/2020 – RTQS 27
9.3.6 Replacement of mechanical parts
In case same mechanical part of the scotch yoke mechanism requires to be replaced, the previous figures
16, 17, 18 and 19 and tables in Section 12 must be used for identification and replacement.
9.3.7 Reassembling of the actuator mechanism in the work shop
Assemble the pneumatic cylinder to the housing tightening with recommended torque shown in the
following table 4 the screws between cylinder and housing.
Assemble the spring cartridge to the housing tightening with recommended torque shown in the following
table 4, the screws between the head flange of spring cartridge and housing.
Replace o-ring at the bottom of the housing making attention there are not dirty or damage on the seal
surface, put the bushing on its seat. Re-assemble scotch yoke and guiding block, make a generous coating
of grease (see next Section 10) on the contact surfaces of yoke and the bushings, assemble the guide bar
after that screw the plug into the housing to complete the bar guide assembling. Tighten the screw between
cylinder piston rod and guiding block, with recommended torque shown in the following Table 4, using a
dynamometric wrench.
Assemble the o-ring, the cover gasket and the cover with all screw.
Table 4
Bolts
Tightening torque
(Nm)
(1)
Bolts
Tightening
torque (Nm)
(1)
M10 40 M30 800
M12 70 M33 1.200
M16 180 M36 1.800
M20 340 M42 3.000
M24 550
M27 700
9.3.8 Reassembling of the actuator on the valve
This activity must be done following the instructions of previous Section 6 of this Manual.
Important
After maintenance operations carry out a few actuator operations to check that
its STROKING is regular and that there is no leak through the seals and fittings.
9.4 Repairs
When maintenance requires substitution of parts, repair must only be carried out with STI’s original spare
parts.
Original spare parts must be required to the STI with reference to the item numbers shown in the next
Section 12.
To ensure that right spare is provided, serial number printed on the RTQS nameplate must be specified
when spares are ordered.
(1)
The torque values in Table 4 have been
calculated considering the standard tie rods or
bolts made in Carbon Steel according to
ASTM A320 grade L7/ASTM A193 grade B7
for tie rods or bolts and ASTM A194 grade 4
for the nuts. Alternative tie rods or bolts in
Stainless Steel are permitted i.e. ASTM A193
B8M (Class 2 or 2C) for bolts/screws and
ASTM A194 grade 8M for the nuts, provided
that yield strength of tie rods or bolts is not
less than 450 MPa.