NPK DG-4 User manual

DEMOLITION GRAB
INSTRUCTION MANUAL
MODELS:
DG-4
DG-6
DG-9
DG-14
DG-16
DG-20/20A
DG-25
DG-30/30A
DG-40/40A
DG-50
“Use Genuine NPK Parts”
7550 Independence Drive
Walton Hills, OH 44146-5541
Phone [phone]
Fax [phone]
© Copyright 2021 NPK Construction Equipment, Inc. www.npkce.com DG000-9600D Demolition
Grab Instruction Manual 6-21 All Models.docx

1
CONTENTS
SAFETY ..........................................................................................................................................................2
OPERATION ...........................................................................................................................................3
MAINTENANCE......................................................................................................................................4
INTRODUCTION.............................................................................................................................................6
EXCAVATOR COMPATIBILITY .....................................................................................................................6
SERIAL NUMBER LOCATION .......................................................................................................................7
SPECIFICATIONS ..........................................................................................................................................8
HYDRAULIC INSTALLATION.........................................................................................................................18
HYDRAULIC LINES................................................................................................................................18
SHUT-OFF VALVES ...............................................................................................................................18
PORT CONNECTION DIAGRAM ...........................................................................................................19
DEMOLITION GRAB HYDRAULIC CIRCUITS...............................................................................................20
MOUNTING INSTALLATION..........................................................................................................................23
MOUNTING TO THE EXCAVATOR .......................................................................................................24
REMOVAL FROM THE CARRIER..........................................................................................................24
STORAGE OF DEMOLITION GRAB..............................................................................................................24
OPERATING INSTRUCTIONS.......................................................................................................................25
OPERATING TECHNIQUES AND PRECAUTIONS...............................................................................27
GENERAL MAINTENANCE............................................................................................................................30
DAILY INSPECTION AND MAINTENANCE...........................................................................................30
ARM MAINTENANCE .............................................................................................................................31
FRAME MAINTENANCE.........................................................................................................................31
FRAME CRACK REPAIR........................................................................................................................31
LUBRICATION POINTS..........................................................................................................................32
SLEWING RING INSPECTION AND MAINTENANCE ..................................................................................33
MEASURING MAXIMUM AXIAL MOVEMENT.......................................................................................33
NPK ASSEMBLY LUBRICANT.......................................................................................................................34
ROTARY JOINT MAINTENANCE ..................................................................................................................35
HYDRAULIC ROTARY JOINT ASSEMBLY............................................................................................35
LEAKAGE OF THE SEALS.....................................................................................................................35
TESTING THE ROTARY JOINT SEALS FOR INTERNAL LEAKAGE...................................................35
REPLACEMENT OF THE SEALS IN THE ROTARY JOINT..................................................................36
TROUBLESHOOTING....................................................................................................................................40
DETERMINE THE TYPE OF PROBLEM................................................................................................40
MEASURING OPERATING PRESSURES.............................................................................................40
RELIEF VALVE CHECKING AND SETTING PROCEDURE..................................................................40
COUNTERBALANCE VALVE LOCATION..............................................................................................42
TROUBLESHOOTING CHART FOR LOW POWER..............................................................................43
CHECKING HYDRAULIC FLOW AT RATED PRESSURE ....................................................................44
PROCEDURE FOR CHECKING HYDRAULIC FLOW AT RATED PRESSURE ...................................44
TROUBLESHOOTING CHART FOR SLOW CYLINDER SPEED..........................................................46
JAW DRIFT .............................................................................................................................................46
TO DETERMINE IF THE JAW DRIFT IS OCCURING FROM A BAD CYLINDER OR THE CARRIER 46
ROTATION..............................................................................................................................................47
MEASURING ROTATION PRESSURES................................................................................................47
ROTATION PRESSURE CHECKING PROCEDURE.............................................................................48
TROUBLESHOOTING CHART FOR ROTATION ..................................................................................48
FASTENER TORQUE CHARTS.....................................................................................................................50
PINION GEAR INSTALLATION......................................................................................................................54
CYLINDER TORQUE SPECIFICATIONS ......................................................................................................55
ROD NUT AND PISTON TORQUES......................................................................................................55
CONVERT FROM DUAL MOTOR TO SINGLE MOTOR (DG20, DG30, DG40) ...........................................56
KEYWORDS FOR COMMON DEMOLITION GRAB COMPONENTS...........................................................57
WARRANTY STATEMENTS ..........................................................................................................................58
NOTES............................................................................................................................................................60
SERVICE RECORD........................................................................................................................................60

2
SAFETY
Safety notices in NPK Instruction Manuals follow ISO and ANSI standards for
safety warnings:
DANGER (red) notices indicate an imminently hazardous
situation which, if not avoided, will result in death or
serious injury.
WARNING (orange) notices indicate a potentially
hazardous situation which, if not avoided, could result in
death or serious injury.
CAUTION (yellow) notices indicate a potentially hazardous
situation, which, if not avoided, may result in minor or
moderate injury.
ATTENTION (blue) notices in NPK Instruction Manuals are
an NPK standard to alert the reader to situations which, if
not avoided, could result in equipment damage.
WARNING –FALLING OR FLYING DEBRIS decals are
included with each NPK Demolition Grab Attachment. The
decal (part number H100-7210) must be installed in the cab,
visible to the operator.
WARNING –STAY CLEAR decal (part number H100-7200)
is installed on all NPK Demolition Grab Attachment. Keep
them clean and visible. NPK will provide decals free of
charge as needed.

3
Warning Decal for Cab Installation
SAFETY
OPERATION
1. Operator personnel must read and understand the NPK INSTRUCTION MANUAL
to prevent serious or fatal injury.
2. FLYING OR FALLING DEBRIS CAN CAUSE SERIOUS OR FATAL INJURY.
Keep personnel and bystanders clear of the DEMOLITION GRAB while in
operation.
3. Do not operate DEMOLITION GRAB without an
impact resistant shield between the DEMOLITION
GRAB and operator. Operate with extreme caution
near walls or columns that may collapse and near
concrete debris that may fall.
4. Operate the DEMOLITION GRAB from the
operator’s seat only.
5. Use two people whenever operator visibility is limited,
one to operate the DEMOLITION GRAB, the other to
guide operations.
6. Do not leave a load suspended in air.
7. Do not pass a load over people, vehicles, etc.
8. Do not operate the DEMOLITION GRAB within
reach of power lines.
9. Do not climb, sit, or ride on the DEMOLITION GRAB.
10. Match the DEMOLITION GRAB size to excavator according to NPK
recommendations, see page 6. The excavator must be stable during DEMOLITION
GRAB operation and during transport.
11. Do not operate without inspection (access) covers in place.
12. Be especially cautious around hydraulic lines. Hydraulic oil can be extremely HOT!
Avoid skin contact with hydraulic oil. It can cause severe burns!
13. Protect hands and body from hydraulic fluids under pressure. Escaping high
pressure fluid can penetrate the skin, causing serious injury. Avoid the hazard by
relieving pressure before disconnecting any lines. Search for leaks with a piece of
cardboard, or other object. If an accident occurs, see a doctor immediately!
Hydraulic fluid injected into the skin must be surgically removed immediately
or gangrene may result!
14. Make daily visual inspections of all fasteners, boom pins, hoses, etc.
15. When removing or installing mounting pins, beware of flying metal chips.

4
SAFETY
MAINTENANCE
1. Use only NPK supplied replacement parts. NPK specifically disclaims any
responsibility for bodily injury or Demolition Grab damage that results from the use
of parts not sold or approved by NPK.
2. Use extreme caution in handling. A fully assembled Demolition Grab can weigh
over 2 tons. Sub-assemblies range in weight from hundreds to thousands of
pounds. To avoid bodily harm, use lifting and securing mechanisms of adequate
capacity to support loads. Seek the aid of an assistant as much as possible, and
always when handling heavier sub-assemblies.
3. The supplied safety bar (t79) MUST always be installed during transport, repairs,
dismounting and mounting to the carrier, changing the cutters and all other routines
at the attachment (GZ).
4. Wear safety glasses and protective clothing when working on the Demolition Grab.
Wear thermal-protective gloves when handling heated parts.
5. Prevent exposure to hazardous fumes. Remove all paint, grease, and oil before
heating, cutting or welding on the Demolition Grab.
6. Be especially cautious around hydraulic lines. Hydraulic oil can be extremely HOT!
Avoid skin contact with hydraulic oil. It can cause severe burns!
7. Protect hands and body from hydraulic fluids under pressure. Escaping fluid
under pressure can penetrate the skin, causing serious injury. Avoid the hazard by
relieving pressure before disconnecting any lines. Search for leaks with a piece of
cardboard, or other object. If an accident occurs, see a doctor immediately!
Hydraulic fluid injected into the skin must be surgically removed within a few
hours or gangrene may result.
8. When removing or installing mounting pins, beware of flying metal chips.

5
SAFETY
MAINTENANCE
STANDARD PRACTICES
Maintenance of and repairs to the Demolition Grab should be performed by an
experienced service technician, thoroughly familiar with all standard practices and
procedures, and most importantly, all safety precautions. The following is a review of
common standard practices to be followed when working with hydraulic equipment and
is not meant to be all-inclusive. Rather, this review is presented as a reminder as to
some of the unique characteristics of hydraulic equipment.
•The prevention of foreign contaminant damage is critical when working with
hydraulic equipment. Protect exposed holes and parts to guard against entry of
contaminants. Install metal or plastic plugs/caps where applicable to prevent entry
of debris into the hydraulic system.
•Mark the location and position of mating parts as an aid to re-assembly. Mark
corresponding parts uniquely to reflect their relationship, including proper location,
position, orientation, and/or alignment.
DO:
•During assembly, observe all markings made during disassembly, and all
corresponding features of mating parts to ensure proper location, position,
orientation, and alignment.
•During disassembly of a sub-assembly, place removed components on a clean, dry
surface, in proper relative position as an aid in re-assembly.
•Always inspect threaded areas on components. Repair or replace as required.
Never apply uncured thread adhesive to a fastener that has cured adhesive on it.
Clean the fastener and the threaded bore. A tap and die may be helpful for this task.
Be sure to remove loose debris from the threaded bore.
•Use care to avoid scratches, nicks, dents, or other damage to machined surfaces of
mating components.
•When securing a component, always tighten cap screws gradually in an opposing
pattern, applying the specified torque.
•Grease can be used to temporarily hold a part in place while the abutting part is
placed into position.
•Always use common sense and exercise standard safety precautions when working
with all tools and equipment required to maintain, repair or troubleshoot the
Demolition Grab.
ATTENTION

6
INTRODUCTION
NPK prides itself on the design and manufacture of high-quality products. This tradition
of quality workmanship and materials continues in our Demolition Grab. Many years of
productive service can be realized with proper operation and care of the Demolition
Grab.
The purpose of this manual is to provide you with the information and instructions
required to properly operate and maintain the Demolition Grab. This will result in
maximum Demolition Grab reliability and productivity.
Read this manual thoroughly before attempting to operate, remove, disassemble,
repair or troubleshoot the Demolition Grab or any of its components.
Follow all the safety precautions contained in this manual. Failure to do so, can
result in death, personal injury, injury to others, and property damage.
EXCAVATOR COMPATIBILITY
These excavator weight ranges are intended as a guideline only. Other factors, such as
stick length, counterweights, undercarriage, etc., must be taken into consideration.
Mounting a Demolition Grab that is too heavy for the excavator can be dangerous and
damage the machine. Verify excavator stability with the Demolition Grab before
transport or operation.
Mounting a Demolition Grab that is too small for the excavator can damage the
Demolition Grab and void Warranties. Please consult NPK Engineering for specific
detailed information.
MODEL
RECOMMENDED EXCAVATOR
CLASS
3rd member mounting
US ton
(Metric ton)
DG-4
3 - 4.5
(2.5 - 4)
DG-6
4.5 - 6.5
(4 - 6)
DG-9
5.5 - 10
(5 - 9)
DG-14
7.5 - 15.5
(7 - 14)
DG-16
11 - 17.5
(10 - 16)
DG-20/20A
15 - 22
(14 - 20)
DG-25
17.5 - 29
(16 - 26)
DG-30/30A
20 - 33
(18 - 30)
DG-40/40A
27.5 - 44
(25 - 40)
DG-50
38.5 - 55
(35 - 50)

7
SERIAL NUMBER LOCATION
DG-4, DG-6, DG-9, DG-14, DG-16, DG-20/20A,
DG-25, DG-30/30A, DG-40/40A, DG-50
sn2 –serial number tag

8
SPECIFICATIONS
MODEL
WEIGHT
CLOSING
CAPACITY
MAXIMUM
FORCE
(volume)
HOIST LOAD
lbs.
(kg)
tonf
(kN)
yd3
(liter)
lbs.
(kg)
DG-4
378
(172)
1.5
(15)
0.12
(90)
1,650
(750)
ROTATION:
Rotation is 360°
FLOW and PRESSURE SPECIFICATIONS:
MODEL
OIL FLOW
PRESSURE
MAIN JAWS
MAIN JAWS
gpm
(lpm)
psi
(bar)
DG-4
4 - 9
(15 - 35)
2,610 - 3,770
(180 - 260)
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-4
3 - 6
(12 - 22)
1,500 –2,000
(103 - 138)
NOTE: Specifications subject to change without notice.

9
SPECIFICATIONS
MODEL
WEIGHT
CLOSING
CAPACITY
MAXIMUM
FORCE
(volume)
HOIST LOAD
lbs.
(kg)
tonf
(kN)
yd3
(liter)
lbs.
(kg)
DG-6
640
(290)
2.1
(21)
0.20
(150)
3,300
(1,500)
ROTATION:
Rotation is 360°
FLOW and PRESSURE SPECIFICATIONS:
MODEL
OIL FLOW
PRESSURE
MAIN JAWS
MAIN JAWS
gpm
(lpm)
psi
(bar)
DG-6
5 - 10
(20 - 40)
2,900 - 4,060
(200 - 280)
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-6
2.5 - 4
(10 - 15)
1,450 - 1,885
(100 - 130)
NOTE: Specifications subject to change without notice.

10
SPECIFICATIONS
MODEL
WEIGHT
CLOSING
CAPACITY
MAXIMUM
FORCE
(volume)
HOIST LOAD
lbs.
(kg)
tonf
(kN)
yd3
(liter)
lbs.
(kg)
DG-9
990
(450)
3.6
(32)
0.24
(180)
3,307
(1,500)
ROTATION:
Rotation is 360°
FLOW and PRESSURE SPECIFICATIONS:
MODEL
OIL FLOW
PRESSURE
MAIN JAWS
MAIN JAWS
gpm
(lpm)
psi
(bar)
DG-9
8 - 13
(30 - 50)
3,190 - 4,640
(220 - 320)
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-9
3 - 4
(12 - 15)
1,450 - 1,885
(100 - 130)
NOTE: Specifications subject to change without notice.

11
SPECIFICATIONS
MODEL
WEIGHT
CLOSING
CAPACITY
MAXIMUM
FORCE
(volume)
HOIST LOAD
lbs.
(kg)
tonf
(kN)
yd3
(liter)
lbs.
(kg)
DG-14
1,415
(642)
4.3
(38)
.39
(300)
6,614
(3,000)
ROTATION:
Rotation is 360°
FLOW and PRESSURE SPECIFICATIONS:
MODEL
OIL FLOW
PRESSURE
MAIN JAWS
MAIN JAWS
gpm
(lpm)
psi
(bar)
DG-14
8 - 16
(30 - 60)
3,625 - 5,075
(250 - 350)
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-14
5 - 8
(20 - 30)
1,450 - 2,030
(100 - 140)
NOTE: Specifications subject to change without notice.

12
SPECIFICATIONS
MODEL
WEIGHT
CLOSING
CAPACITY
MAXIMUM
FORCE
(volume)
HOIST LOAD
lbs.
(kg)
tonf
(kN)
yd3
(liter)
lbs.
(kg)
DG-16
1,930
(875)
5.4
(48)
.56
(425)
7,716
(3,500)
ROTATION:
Rotation is 360°
FLOW and PRESSURE SPECIFICATIONS:
MODEL
OIL FLOW
PRESSURE
MAIN JAWS
MAIN JAWS
gpm
(lpm)
psi
(bar)
DG-16
16 - 26
(60 - 100)
3,625 - 5,075
(250 - 350)
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-16
5 - 8
(20 - 30)
1,450 - 2,030
(100 - 140)
NOTE: Specifications subject to change without notice.

13
SPECIFICATIONS
MODEL
WEIGHT
CLOSING
CAPACITY
MAXIMUM
FORCE
(volume)
HOIST LOAD
lbs.
(kg)
tonf
(kN)
yd3
(liter)
lbs.
(kg)
DG-20/20A
2,756
(1,250)
6
(52)
.65
(500)
9,920
(4,500)
ROTATION:
Rotation is 360°
FLOW and PRESSURE SPECIFICATIONS:
MODEL
OIL FLOW
PRESSURE
MAIN JAWS
MAIN JAWS
gpm
(lpm)
psi
(bar)
DG-20/20A
16 - 26
(60 - 100)
3,625 - 5,075
(250 - 350)
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-20/20A
8 - 13
(30 - 50)
1,450 - 2,030
(100 - 140)
OPTIONAL SINGLE MOTOR
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-20/20A
5 - 8
(20 - 30)
1,450 - 2,030
(100 - 140)
NOTE: Specifications subject to change without notice.

14
SPECIFICATIONS
MODEL
WEIGHT
CLOSING
CAPACITY
MAXIMUM
FORCE
(volume)
HOIST LOAD
lbs.
(kg)
tonf
(kN)
yd3
(liter)
lbs.
(kg)
DG-25
3,216
(1,450)
6
(60)
.78
(600)
9,920
(4,500)
ROTATION:
Rotation is 360°
FLOW and PRESSURE SPECIFICATIONS:
MODEL
OIL FLOW
PRESSURE
MAIN JAWS
MAIN JAWS
gpm
(lpm)
psi
(bar)
DG-25
16 - 26
(60 - 100)
3,625 - 5,075
(250 - 350)
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-25
8 - 13
(30 - 50)
1,450 - 2,030
(100 - 140)
OPTIONAL SINGLE MOTOR
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-25
5 - 8
(20 - 30)
1,450 - 2,030
(100 - 140)
NOTE: Specifications subject to change without notice.

15
SPECIFICATIONS
MODEL
WEIGHT
CLOSING
CAPACITY
MAXIMUM
FORCE
(volume)
HOIST LOAD
lbs.
(kg)
tonf
(kN)
yd3
(liter)
lbs.
(kg)
DG-30/30A
4,078
(1,850)
8.1
(72)
1.05
(800)
12,125
(5,500)
ROTATION:
Rotation is 360°
FLOW and PRESSURE SPECIFICATIONS:
MODEL
OIL FLOW
PRESSURE
MAIN JAWS
MAIN JAWS
gpm
(lpm)
psi
(bar)
DG-30/30A
21 - 32
(80 - 120)
3,625 - 5,075
(250 - 350)
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-30/30A
8 - 13
(30 - 50)
1,450 - 2,030
(100 - 140)
OPTIONAL SINGLE MOTOR
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-30/30A
5 - 8
(20 - 30)
1,450 - 2,030
(100 - 140)
NOTE: Specifications subject to change without notice.

16
SPECIFICATIONS
MODEL
WEIGHT
CLOSING
CAPACITY
MAXIMUM
FORCE
(volume)
HOIST LOAD
lbs.
(kg)
tonf
(kN)
yd3
(liter)
lbs.
(kg)
DG-40/40A
4,519
(2,050)
8.1
(72)
1.18
(900)
12,125
(5,500)
ROTATION:
Rotation is 360°
FLOW and PRESSURE SPECIFICATIONS:
MODEL
OIL FLOW
PRESSURE
MAIN JAWS
MAIN JAWS
gpm
(lpm)
psi
(bar)
DG-40/40A
21 - 32
(80 - 120)
3,625 - 5,075
(250 - 350)
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-40/40A
8 - 13
(30 - 50)
1,450 - 2,030
(100 - 140)
OPTIONAL SINGLE MOTOR
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-40/40A
5 - 8
(20 - 30)
1,450 - 2,030
(100 - 140)
NOTE: Specifications subject to change without notice.

17
SPECIFICATIONS
MODEL
WEIGHT
CLOSING
CAPACITY
MAXIMUM
FORCE
(volume)
HOIST LOAD
lbs.
(kg)
tonf
(kN)
yd3
(liter)
lbs.
(kg)
DG-50
5,512
(2,500)
10.1
(90)
1.44
(1100)
12,125
(5,500)
ROTATION:
Rotation is 360°
FLOW and PRESSURE SPECIFICATIONS:
MODEL
OIL FLOW
PRESSURE
MAIN JAWS
MAIN JAWS
gpm
(lpm)
psi
(bar)
DG-50
26 - 37
(100 - 140)
3,625 - 5,075
(250 - 350)
MODEL
OIL FLOW
PRESSURE
ROTATION
ROTATION
gpm
(lpm)
psi
(bar)
DG-50
8 -13
(30 - 50)
1,450 - 2,320
(100 - 160)
NOTE: Specifications subject to change without notice.

18
HYDRAULIC INSTALLATION
HYDRAULIC LINES
Typically, the pressure line to close is arranged on the left side of the boom and the
open line is on the right side.
SHUT-OFF VALVES
Some hydraulic installation kits use two shut-off valves (k4) on the dipper stick (k1) of
the carrier. These valves control the hydraulic oil going to the close side (m3) and the
open side (m4) from the Demolition Grab attachment.
Pressure test ports (k8) are in the shut-off valves (k4). Each shut-off valve has an “ON”
(k5) and an “OFF” (k6) position.