A single-stroke pneumatic apparatus incorporates a hollow cylindrical frame 1) with inlet and outlet ports (2,3). A handgrip (4) containing a directional flow control (5) is attached to the upper end of the frame. A striker (6) is provided in the bore of the frame (1) with provision for reciprocating back and forth so as to divide this bore into a forward-stroke chamber (8) a back-stroke chamber (7). A tool (9) is supported in the lower end of the frame (1). A shell (10) with holes (11) surrounds the frame (1) from the outside, forming a muffling chamber (12) therewith, within a full length of the stroke of the striker (6). Additional outlet ports (15) are provided in the lower end of the frame (1) which communicate the back-stroke chamber (8) with the muffling chamber (12) located wherein is a filter (6) overlapping the holes (11) in the shell (10).

BACKGROUND OF THE INVENTION 
Field of the Invention 
The present invention relates to pneumatic apparatus of the percussive type 
used in construction, mining, mechanical engineering and metallurgy and 
has specific reference to single-stroke pneumatic apparatus. 
Description of the Prior Art 
Single-stroke pneumatic apparatus commonly employed for marking, 
centre-pricking, marking-off and chiselling off risers are pneumatic 
hammers. The tool the hammer is fitted with varies with the application. 
It can be a stamp, a prick-punch, a hobby or a chisel. The tool is 
supported in a hollow frame with inlet and outlet ports and a striker 
dividing the frame bore into forward- and working-stroke chambers. A 
directional flow control is provided on the frame. The source of energy is 
compressed air fed from a mobile or stationary compressor over a flexible 
hose. In operation, the compressed air admitted into the chambers of the 
frame with the aid of the directional flow control manipulated by the 
operator, causes the striker to reciprocate back and forth axially and 
deliver cyclewise blows at the end face of the tool. The work done by the 
tool materializes in any of the following operations depending on the type 
of the tool: marking, centre-pricking, chiselling or riveting. 
The atmosphere at the working place where pneumatic hammers are in use is 
commonly laden with dust and the operator cannot but stay in such a 
surrounding. Therefore, the problem of increasing the reliability of the 
pneumatic hammer is one of great concern. 
Known in the art is a single-stroke pneumatic apparatus (cf. USSR 
Inventor's Certificate No. 781048, IPC B25D 9/14, 1980) comprising a 
hollow cylindrical frame provided with inlet and outlet ports, and a 
striker recurrently interacting with a resilient means located at an end 
face of the frame. The directional flow control is a solenoid-actuated 
valve operated by a microswitch. The valve made up of three parts lacking 
a mechanical link with each other is of intricate design. Apart from that, 
the known apparatus lacks reliability, for dust and other fine particles 
are sucked into the bore of the frame through the outlet ports when the 
striker is on a back stroke. The noisy high-velocity exhaust from the 
apparatus creates trying labour conditions for the operator. 
Also known is a single-stroke pneumatic apparatus, i.e. a pneumatic hammer 
(cf. German Patent No. 671,958, Cl. 87b 2/11, 1939) comprising a hollow 
cylindrical frame with inlet and outlet ports, a spring-loaded striker 
forming forward- and back-stroke chambers in the frame bore, a handgrip 
located wherein is a directional flow control and a tool fixed in the 
upper end of the frame. 
In the known apparatus, the outlet ports are laid out in a way which cannot 
prevent ingress of dust-laden atmosphere into the frame bore. Therefore, 
the hammer cannot last long. The noisy exhaust from the apparatus creates 
trying labour conditions for the operator. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a single-stroke pneumatic 
apparatus, in which an enhanced reliability and improvements in the 
service conditions thereof would be ensured by the design of the 
air-distribution means. 
The invention includes a single-stroke pneumatic apparatus comprising a 
hollow cylindrical frame with inlet and outlet ports, a handgrip attached 
to the upper end of the frame, a directional flow control located in the 
handgrip and used to admit compressed gaseous fluid recurrently into the 
bore of the frame, a striker located in the bore of the frame with 
provision for reciprocating back and forth so as to divide the bore of the 
frame into a forward-stroke chamber--admitted recurrently through the 
inlet ports is compressed gaseous fluid--and a back-stroke chamber, a 
return spring fitted to the striker at that end thereof which faces the 
back-stroke chamber, a tool attached to the lower end of the frame, and a 
shell with holes which surrounds the frame and forms therewith a muffling 
chamber communicating with the atmosphere via the holes in the shell and 
with the back-stroke chamber via the outlet ports. According to the 
invention the shell extends through a full length of stroke of the 
striker, the frame is provided at its lower end with additional outlet 
ports which connect the back-stroke chamber to the muffling chamber and a 
filter is provided in the muffling chamber which overlays the holes in the 
shell--located on a level therewith--and serves as a muffler when the 
stroker displaces towards its lowermost position. 
The apparatus of the above design is protected against an ingress of dust 
and other fine particles into the bore of the frame and therefore lasts 
longer than any known prior art devices. It also effectively muffles the 
noise in operation, creating satisfactory labour conditions, owing to the 
presence of the filter through which gaseous fluid is exhausted.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2, a single-stroke pneumatic apparatus comprises a 
hollow cylindrical frame 1 with inlet and outlet ports 2, 3. A handgrip 4 
is immovably attached to the upper end of the frame 1. A directional flow 
control 5 is contained inside the handgrip 4. A striker 6 is provided in 
the bore of the frame 1 with provision for reciprocating back and forth so 
as to divide the bore of the frame 1 into a forward stroke chamber 7 and a 
back-stroke chamber 8, and a tool 9 is attached to the lower end of the 
frame 1. An immovable shell 10 with holes 11 surrounds the frame 1 from 
the outside all through the length of the striker stroke and forms in the 
frame a muffling chamber 12 which communicates with the atmosphere via the 
holes 11 in the shell 10 and with the back-stroke chamber 8 via the outlet 
ports 3. Mounted in the bore of the frame 1 on the side of the back-stroke 
chamber 8 are a return spring 13 cooperating with the striker 6 and a 
shock-absorbing stop 14. Additional outlet ports 15 are provided in the 
lower end of the frame 1 which connect the back-stroke chamber 8 to the 
muffling chamber 12, and a filter 16 is provided in the muffling chamber 
12 on a level with the holes 11. 
The apparatus operates in the following manner. 
Compressed gaseous fluid is admitted into the forward-stroke chamber 7 via 
a union in the handgrip 4 (FIG. 1) the directional flow control 5 and the 
inlet ports 2 when a trigger 17 is being depressed (FIG. 1). At the said 
time, the back-stroke chamber 8 is connected to the atmosphere via the 
outlet ports 3, the additional outlet ports 15, the muffling chamber 12, 
the filter 16 and the holes 11. The striker 6 is acted upon by the 
compressed gaseous fluid in the forward-stroke chamber 7 travels downwards 
against the action of the return spring 13, whereby the gaseous fluid 
contained in the back-stroke chamber is expelled into the muffling chamber 
12 through the additional outlet ports 15 and hence into the atmosphere via 
the filter 16 and the holes 11. As soon as the top edge of the travelling 
striker 6 uncovers the outlet ports 3, the gaseous fluid contained in the 
forward-stroke chamber 7 escapes into the atmosphere through the outlet 
ports 3, the filter 16 and the holes 11. At this stage, the filter 16 
functions as the muffler. Continuing on the down stroke, the striker 6 
delivers a blow at the end face of the tool 9 in contact with the work, 
causing it to do the job. The outlet ports 3 relieve the striker 6, and 
consequently the tool 9, of a continuing pressure which may cause the tool 
9 to bounce, losing contact with the work. The flow section and number of 
the outlet ports 3 should be selected so that the pressure buildup in the 
forward-stroke chamber 7 is higher than the maximum force of the 
compressed return spring 13. Otherwise the apparatus will not function. 
When the trigger 17 is released, no compressed gaseous filud enters the 
forward stroke chamber 7 and this becomes connected to the atmosphere via 
the outlet ports 2 and the directional flow control 5. As the striker 6 is 
returned into the topmost position due to the action of the return spring 
13, air is sucked into the back-stroke chamber 8 through the holes 11, the 
filter 16, the muffling chamber 12 and the additional outlet ports 15. The 
filter 16 separates dust from the air, keeping the dust outside the 
back-stroke chamber 8. 
The disclosed apparatus compares favourably with the known single-stroke 
pneumatic apparatus in that it prevents ingress of dust and other fine 
particles inside the frame and operates at a significantly lower noise 
level. 
These advantages add 10-15% to the apparatus' reliability and improve 
labour conditions. 
The invention can be used to advantage in coping with such jobs as marking 
and marking-off, centre-pricking, riveting and chiselling off risers. 
It may also be of utility in trimming roofs of mine openings, punching 
holes, breaking concrete and other civil engineering applications.