CHAPTER 3
THEORY OF OPERATION
3-1. GENERAL.
This chapter contains a theory of operation for the
Pakhammer enabling maintenance personnel to
more effectively understand and troubleshoot the
Pakhammer in the event of a malfunction. The
cutaway illustration, figure 3-1, is to be used in
conjunction with the following theory of operation.
The Pakhammer is a portable (lightweight, and
easily handled and operated), pneumatic impact tool
designed for forcible entry during rescue and
firefighting operations. Operating air may be
obtained from either an air compressor or air
cylinder. By varying the pressure of the operating
air, the impact force of the blows generated by the
Pakhammer can be used for a variety of different
purposes. The pressure range over which the
Pakhammer will operate is 40 to 200 psi (2.8 to 13.8
bar) resulting in approximately 1050 blows per
minute at a 200 psi pressure with consumption of 19
scfm (538 l/m).
3-2. GENERAL CONSTRUCTION.
The Pakhammer cylinder, handles, valve body and
valve cover are fabricated from aluminum alloy. The
piston rod and springs are fabricated from alloy
steel. All fasteners are stainless steel. Components
of the tool retainer assembly are hardened steel
alloy.
3-3. THEORY OF OPERATION.
a.
The Pakhammer is activated by pulling
(squeezing) the trigger lever (part of the pistol
grip handle) permitting external operating air to
enter the handle assembly through the oiler and
hose assembly threaded connection. As
external operating air passes through the oiler,
a controlled volume of lubrication is picked up with
the air to maintain continuous fog lubrication of the
Pakhammer internal components during operation.
b.
Operating through a trigger link, the normally spring
closed trigger valve plunger unseats permitting
operating air to enter, through an air inlet
passageway, the shuttle body chamber at the rear
of the piston rod. The piston rod is restrained in a
rearward position by two piston return springs. The
compressed air at the rear of the piston rod propels
the piston rod forward striking the installed tool bit to
drive it forward while simultaneously driving the
shuttle valve rearward to seal the exhaust ports in
the shuttle valve body.
c.
As the piston rod is propelled forward and passes
the pilot tube port, compressed air is conveyed
through the pilot air passage to the rear of the shuttle
valve driving it forward sealing the air inlet
passageway to the rear of the piston rod while
simultaneously opening the exhaust ports to
evacuate any residual internal compressed air to the
atmosphere.
d.
With no air pressure at the rear of the piston rod, the
piston rod is returned to its rearward position by the
piston return springs. The button at the rear of the
piston rod contacts the shuttle valve and drives it
rearward to again open the air inlet passageway to
the rear of the piston rod and seal the exhaust ports
in preparation for another operating cycle. This
operating cycle will repeat until the trigger lever is
released, seating the trigger valve plunger and
sealing the air inlet port thereby preventing external
operating air from entering the air inlet passageway.
Figure 3-1. Cutaway of Pakhammer
3-1/(3-2 blank)
