Moog D680 Series - Page 8

8Rev. C, April 2017
INTRODUCTION Moog D680 Series Proportional Control Valves
DESCRIPTION OF OPERATION
8
INTRODUCTION
Rev. C, April 2017
Moog D680 Series Proportional Control Valves
DESCRIPTION OF OPERATION
Applications with Safety Requirements (Fail-safe)
Selecting the Fail-safe Function for Applications
with Safety Requirements
The valve series D680 is offered with various fail-safe
functions. The behavior of the valve in a fail-safe situa-
tion depends on the fail-safe function selected, the pilot
valve and the actual pilot pressure, the electrical supply
of the valve electronics and the 4/2-way valve. The tables
provide further details to help select the best fail-safe
function for your machine.
The spool positions of the main stage in the event of a
failure of valve electronics, control pressure or power
supply are described below.
D683/D684 valve with integrated 4/2-way solenoid valve for
applications with safety requirements
Fail-safe
function
Spool position of the main stage Pilot pressure
1) 2)
Valve electronics 4/2-way valve
F End position P → B and A → T On Off –
Undefined Off On –
End position P → B and A → T Off Off –
D End position P → A and B → T On Off –
Undefined Off On –
End position P → A and B → T
(D681: 20 % P → A and B → T)
Off Off –
W Undefined On Off On
Undefined Off On On
Undefined Off Off On
Defined center position On Off Off
Defined center position Off On Off
Defined center position Off Off Off
U End position P → B and A → T On Off On
Undefined Off On On
Defined center position or defined
P → B and A → T
Off Off On
Defined center position or defined
P → B and A → T
On Off Off
Defined center position or defined
P → B and A → T
Off On Off
Defined center position or defined
P → B and A → T
Off Off Off
1) System pressure for internal pilot connection
2) Pressure “off” means without pressure (<<1 bar). For higher pressures the spool position of the main stage is undefined. Pressure
“on” means a pilot pressure of at least the value caculated according to the procedure given in the section “Pilot Pressure and Flow
Calculation”. For lower pressures the spool position of the main stage is undefined.
X YT A P B
T
V
B
V
P
V
A
V