W
WW
O
O
OO
O
O
O
OO
W
W
WW
W
W
Certain models of 21 through 27 Series pumps and motors were originally produced with plastic filled cylinder block
piston assemblies. Certain Series 20 back-to-back transmissions were produced with hollow cylinder block piston
assemblies. Certain models of 21 through 23 Series pumps and fixed motors are now being produced with solid
cylinder block piston assemblies. To simplify spare parts inventory for these units, welded piston assemblies are
provided as spare parts.
When replacing plastic filled, hollow, or solid pistons with welded pistons during overhaul or repair of a unit, it is
mandatory that the welded pistons be incorporated symmetrically in multiples of three (3)[either three (3), six (6), or
all nine (9)] in order to assure the block assembly remains in balance and speed capability is not adversely affected.
Units originally equipped with welded piston assemblies MUST be repaired with welded piston assemblies.
When replacing plastic filled, hollow, or solid pistons with welded pistons during
overhaul or repair of a unit, it is mandatory that the welded pistons be incorporated
symmetrically in multiples of three (3)
.
-OR-
W = Welded
O = Other
End View of Solid, Welded, Hollow, and Plastic Filled
Piston Assemblies
Solid
Piston
Assembly
Plastic
Filled
Piston
Assembly
Welded
Piston
Assembly
Hollow
Piston
Assembly
© Danfoss, 2013 BLN-9736 • Rev BA • September 2013 1
Service Kit Instructions
Series 20
Incorporating welded piston assemblies
WARNING
Due to their higher mass, solid pistons reduce the speed capabilities of the pump or motor in which they
are installed by approximately 20%. Solid pistons MUST NOT be sold as spare parts or be installed in pumps
or fixed motors which were originally equipped with plastic filled, hollow, or welded pistons. Operating a
hydrostatic pump or motor at speeds above its rated capability may cause loss of hydrostatic braking
capacity.
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1
