General Instructions; Keep It Clean; Inspect For System Contamination; Replace The O-Rings And Gaskets - Danfoss 51 Series Service Manual

Service Manual
Introduction

General Instructions

General Description

Series 51 Electrohydraulic Proportional Controls Service Manual

Keep it Clean

You can complete many repairs or adjustments without removing the unit from the machine, if the unit is
accessible and you can thoroughly clean it before beginning any procedures.
Cleanliness is a primary means of assuring satisfactory motor life on either new or repaired units. Clean
the outside of the motor thoroughly before disassembly. Take care to avoid contamination of the system
ports. Cleaning parts with a clean solvent wash and air drying is usually adequate.
As with any precision equipment, keep all parts free of foreign materials and chemicals. Protect all
exposed sealing surfaces and open cavities from damage and foreign material. Cap all hoses after
removal, and plug all open ports. Cover any unattended parts with a protective layer of plastic.

Inspect for System Contamination

Inspect the motor for signs of system contamination. If you find contamination, fully disassemble, clean
and inspect all components of the motor.

Replace the O-rings and Gaskets

Replace all O-rings and gaskets. Discard them only after you make certain that you have the correct
replacement parts. Lightly lubricate all O-rings with clean petroleum jelly before assembly.

Lubricate all Moving Parts

During reassembly, coat all moving parts with a film of clean hydraulic oil. This helps lubricate the
surfaces during start-up.
For fluid quality requirements, refer to Hydraulic Fluids and Lubricants, Technical Information 520L0463.

Torque Procedure

During reassembly, cross torque all retaining screws to the given value. Do not overtorque.

Overview

Electrohydraulic proportional controls infinitely vary motor displacement between maximum and
minimum. They do this by shifting the 4-way valve. The spool position shifts with an
•
electric pressure-reducing valve. It varies signal pressure on the end of the 4-way valve (D7, D8
controls), or
•
electrically varied differential pressure on the ends of a piston connected to the 4‑way valve (EP, EQ,
ER, ES, ED, EE controls), or
•
electric proportional solenoid acting directly on the 4-way valve (A7, L1, L2, L7 controls).

Multifunction Block

Some of the electrohydraulic proportional controls are used in conjunction with the multifunction block.
The multifunction block is a manifold with a shuttle valve that routes high loop (system pressure) from
port A or B to the 4-way valve while routing the low loop (stystem pressure) to the PCOR valve. The 4-way
valve directs this pressure to the ends of the servo piston to change displacement. The multifunction
block may also provides the pressure compensating override (PCOR) option that regulates system
pressure.
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