Piston seal cartridge for a reciprocating needle

An air operated dispense head for dispensing of hot melt and related adhesives is provided which utilizes a drop-in seal cartridge assembly in which a hardened needle is sealed using a pair of quad seals along with soft back up rings. Improved life is obtained from this combination of elements.

BACKGROUND OF THE INVENTION 
Air operated dispensing heads for the dispensing of various fluids such as 
hot melt adhesive are, of course, well known and have been in common use 
for many years. Such heads must operate reliably and accurately at 
relatively elevated pressures (up to 1,000 PSI) and at relatively rapid 
activation rates (5,000 cycles per minute). Industry standard cartridges 
are generally pressed in or screwed into the housing. Such construction 
often leads to the galling and seating of the cylinder in normal long term 
usage as seen presently. 
It is therefore an object of this invention to provide an air operated 
dispense head which is capable of extended life and yet which is easy to 
assemble and manufacture. 
SUMMARY OF THE INVENTION 
An air operated dispense head is provided wherein the needle is formed of a 
hardened stainless steel and is guided by a pair of internal quad seals 
one of which is backed up by soft back up rings formed of a Rulon.RTM. 
material. 
The cartridge is located in the dispense head housing with some diametrical 
clearance using external static elastomeric seals. It is further located 
and held in place by captive shoulder bolts which are removable by hand. 
This self-alignment construction allows the cartridge to be centered by or 
concentric with the piston as it is inserted within the cartridge thereby 
minimizing side loading and accordingly increasing seal life. The industry 
standard constructions do not allow for self alignment and therefore 
inevitably result in seal side loading which results in reduced seal life. 
These and other objects and advantages of the invention will appear more 
fully from the following description made in conjunction with the 
accompanying drawings wherein like reference characters refer to the same 
or similar parts throughout the several views.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The cartridge of the instant invention is generally designated 10 as shown 
in FIG. 1 and is comprised of a generally cylindrical body 12, a hardened 
needle piston 14, first and second quad seals 16 and 18 respectively, 
backup rings 20 and 21 and external seals 22. Cartridge 10 is utilized in 
an air operated dispense head 11 as shown more generally in FIG. 2 
Body 12 is provided with an interior bore 12a which serves to accommodate 
the needle 14. Bore 12a has a pair of grooves 12b located therein. The 
groove width (that is axial length) is not particularly critical however 
the depth of the groove is and toward that end, a groove 12b having a 
diameter of 0.247 inches is the preferred embodiment in association with 
the various dimensions suggested hereinafter. 
A pair of grooves 12c are located in the outer circumference of body 12 and 
serve to accommodate external static seals 22. Needle 14 is formed ideally 
of a 440C stainless steel which forms a very hard and long-wearing 
surface. 
First and second quad seals 16 and 18 are so named because of their 
cloverleaf appearance in cross section. Such seals are desirably formed 
from a Viton.RTM. v884-75 material which is a fluorinated rubber material 
manufactured by DuPont. 
Backup rings 20 and 21 are generally annular in shape and are manufactured 
from Rulon.RTM. "A" fluoropolymer, a material manufactured by Dixon 
Industries. Rulon.RTM. is a fiber filled Teflon.RTM. type material and is 
relatively soft (having a durometer reading of 70 on the Shore D scale) 
compared to normal type backup rings which are manufactured from metal or 
very hard rubbers. The particular combination of elements disclosed in 
this application has yielded substantially improved results over prior art 
devices. The device of the instant invention yields life before leakage of 
4 to 5 times the previous best known industry standard devices. 
Quad seals 16 and 18 have a free inside diameter of 0.114 inches and an 
outside diameter of 0.254 inches. Needle 14 has a diameter of 0.125 inches 
in the preferred embodiment. 
The cartridge 10 is held in module 26 by means of shoulder bolts 28 which 
locate body 12 by means of slots 30 cut therein. Because of the external 
and internal seal arrangement, the device is self-aligning which helps 
prevent side loads on the needle and seals and yields the extended life 
experienced. 
It is contemplated that various changes and modifications may be made to 
the dispense head without departing from the spirit and scope of the 
invention as defined by the following claims.