J&M 220 Operating And Maintenance Manual - page 51

MODEL 220 

HYDRAULIC 

IMPACT HAMMER 

V. HYDRAULIC 

CIRCUITRY 

A.  DRIVE PUMP (CONTINUED) 

After the upward movement of the ram stops, it begins to fall because the DUMP 

VALVE is already open.  While the ram is falling, and during the deceleration phase 

of the cycle, pump flow is stored in the PRESSURE ACCUMULATOR.  While the 

ram is falling, the CONTROL VALVE is held in its shifted position by a pilot signal 

generated by the DUMP VALVE.  Oil exiting the DUMP VALVE, at high speed, 

goes directly to the blind end of the CYLINDER and does not restrict the downward 

movement of the ram.  When the ram impacts the pile, the downward movement of 

the cylinder stops, and the pilot signal is removed from the CONTROL VALVE.  A 

spring returns the CONTROL VALVE to its normal (lift) position, and another lift 

cycle begins.  The CYLINDER will continue cycling, as described above, until the 

DIRECTIONAL CONTROL VALVE (V2) is de-energized by returning the 

FORWARD/REVERSE switch to the NEUTRAL position.  When the trip valve is 

activated by the trip bar, a pilot pressure signal is sent to the CONTROL VALVE 

(V3) pilot piston, shifting the CONTROL VALVE.  The balance of the cycle is the 

same as in the long stroke position, above. 

B.  STROKE CONTROL PUMP 

With the diesel engine running, hydraulic oil is taken from the reservoir by the 

stroke control pump (P2).  The stroke control pump oil returns to the reservoir if the 

clamp switch is in the NEUTRAL position.  Returning oil is filtered by the return filter 

(F2). 

Turning the clamp switch to CLOSE retracts the variable stroke cylinder (CLY2).  

Returning the switch to neutral allows the hammer to run at that stroke length.  

Turning the clamp switch to OPEN momentarily, extends the variable stroke 

cylinder (CLY2)  Pressure is indicated by the pressure gage (GA-2).  Pilot pressure 

in the stroke control circuit is limited to 1500 PSI (103 Bar) by the STROKE RELIEF 

valve (RV2).  Adequate pressure to extend and retract the variable stroke cylinder 

is insured by relief valve (RV2). 

The quick-disconnect coupler (QD3 and QD4) permits de-coupling of the stroke 

control hose at the power pack. 

V-2