Sheffer MH SERIES - Manual (Page 5)

Sheffer pioneered tapered cushions,
designed to provide gradual decelera-
tion and eliminate shock upon entrance
of the cushion pistons, have now been
considerably improved. The tapered
cushion has been married with a fine
thread, wide range, adjusting screw.
This new combination offers a positive,
low-shock deceleration and a method
to adjust the cushioning effect for
speeds and loads.
The adjusting screw is identified by a
tag affixed to the head (or cap) and can
be further distinguished by a cross-slot
in the head of the screw. It does not
project beyond the surface of the head
(or cap) through its full range of
adjustment so no clearance need be
considered on close fit installations.
The adjusting screw and the cushion
check can be interchanged in the same
cylinder end. This flexibility can be
important if, after installation, it is
discovered that the adjusting screw is
inaccessible.
The cushion check, which does not
require adjustment, has a single slot in
its head. It does not project beyond
the surface of the head (or cap). The
cushion check plus the tapered cushion
piston provides rapid acceleration out
of cushioning. There is no spring in the
cushion check to fatigue, hence, no
worry of mechanical failure.
Cushioning is designed to properly
cushion the cylinder and is not intended
to cushion large inertia loads. Cushions
do not substitute for speed controls or
deceleration valves on most installations.
As indicated on page MA-6, the
standard positions for ports are 1 and 5.
Where possible, the standard positions
for cushion adjusting screws will be 2
and 6 and the standard positions for
cushion checks will be 4 and 8. With
some mounting styles, it is not possible
to so locate the adjusting screws and
checks. For example, a Trunnion Front
Mount has the trunnion pins located in
positions 2 and 4 on the head. With the
port in position 1, the only side
available for both adjusting screw and
check is position 3. Since both will then
be located on the same side, they will be
located off-center. This example would
hold true with the TR, CL, FHF and
RHF mounts. See
Chart A for standard
positions that will be supplied unless
otherwise specified. When requested,
other positions can be supplied so long
as there is no interference with
mounting.
Where access to an adjusting screw
or check could be made difficult
because of proximity to a mount, the
locations of the screws will be slightly
off-center. An example of this would
be a small bore cylinder with a side lug
mount.
Because of space limitations, neither
cushion adjusting screws nor cushion
ball checks can be put into 1
1 / 2 " and
2", 2 1 / 2 " bore sizes for cushioned front
when they are specified with 2:1 rod
diameters.
The chart below shows the recommended
working pressures for MH Series cylinders
by bore and rod diameters. Note that the
column“Operating Pressure” is based on a
3:1 safety factor. It is felt that this is an
adequate safety factor for any well
designed hydraulic system where shock
conditions have been considered and
reduced to an acceptable level.
The “Max. Shock Service” column is
based on a 2:1 safety factor and SHOULD
NOT be used to determine operating
pressures.
All values on the adjacent chart are
based on the cylinder as a pressure
vessel. Use of the proper mounting style
to withstand the thrust generated must
be considered.
The following factors in shock loading
should be considered:
I Relief valves in the circuit do not
protect the components from shock
because of the time lag.
I Gauges do not necessarily register
shock conditions, either because of
their location in the circuit, or the
short duration of the shock.
I The two general types of shock loading
to be considered are pressure rise
caused by quick stop of the flow in
the circuit and quick pressure drop.
Decompression shock is particularly
important in large bore cylinders and
can be as destructive as compression
shock.
Cushions Pressure and Shock
OPERATING MAX. SHOCK
PRESSURE SERVICE
PISTON 3:1 SAFETY FACTOR 2:1 SAFETY FACTOR
BORE ROD BASED ON YIELD BASED ON YIELD
SIZE DIAMETER IN PSI IN PSI
1 1 / 8 5 / 8 3,600 5,400
1 1 / 2 ALL 2,250 3,375
5 / 8 1,400 2,100
1, 1 3 / 8 2,450 3,675
5 / 8, 1 900 1,350
1 3 / 8, 1 3 / 4 1,550 2,325
3 1 / 4 ALL 1,400 2,100
4 ALL 925 1,390
1, 1 3 / 8, 1 3 / 4 675 1,000
BALANCE 1,075 1,600
6 ALL 800 1,200
1 3 / 8, 1 3 / 4 625 940
BALANCE 875 1,300
1 3 / 8, 1 3 / 4 475 700
BALANCE 675 1,000
8
7
5
2 1 / 2
2
Cushions and Pressure
CUSHION
ADJUSTING CUSHION
MOUNT SCREW CHECK
TF AND FHF 3 and 6 3 and 8
CL 3 and 7 3 and 7
TR AND RHF 2 and 7 4 and 7
ALL OTHER
MOUNTS 2 and 6 4 and 8
Standard positions for cushion adjusting screws
and cushion checks in relation to port positions
by style of mounting.
Chart A
Position Diagram for Ports,
Air Bleeds, Cushion Adjusting
Screws and Cushion Checks
1
2
3
4
5
6
7
8
9
Maximum Pressure Ratings
Specifications
Cylinder Weight Chart
BORE 1 1 / 8 1 1 / 2 2 2 1 / 2 3 1 / 4 4 5 6 7 8
ZERO STROKE 3 6 8 11 22 30 45 70 85 100
ADD PER INCH
OF STROKE .25 .35 .6 .9 .9 1.2 1.7 2.5 3 4
NOTE: The above weights are based on an average value for cushioning, rod side, and the various types of
mountings for uncrated cylinders to establish approximate shipping weights. Add 10% of cylinder weight to
determine estimated weight of crated cylinder.
1 MH-4