Dixon Valve 50 TON RAM Complete Manual - Manual (Page 5)

50 Ton Ram Instruction Manual
Holedall Concept 1
The Concept of the Holedall Coupling
Applied with the Ram
The application of Holedall couplings to hose is best described as a draw type progressive swage. This
swaging of the coupling to the hose is accomplished by pushing the tubular ferrule (normally made of tubular
steel, but also available in brass or stainless steel) through a split die which reduces the ferrule O.D. causing the
ferrule to penetrate into the hose wall. This results in a 360° uninterrupted compression band around the hose.
The patented Holedall coupling includes a hose stem and a ferrule. The hose stem is of a conventional
serrated design, including a collar which locks the ferrule to the stem. The tubular ferrule will include a top
(outboard) row of holes and, depending on style of ferrule, a bottom (inboard) row of holes and a series of
serrations (if present, depending upon style) inside. The purpose or design function of the holes and serrations
(if present, depending upon style) is as follows:
1. Upon insertion of the stem into the hose, prior to the swage, the top (outboard) row of holes affords positive
proof, attained by visual inspection, that the stem portion of the coupling is fully inserted into the hose.
2. The ferrule holes and serrations provide additional holding power to the coupling.
This is effected as follows:
The Holedall coupling is applied directly to the raw end of the hose without, in any manner, altering the
hose cover. The hose cover need not be skived or buffed off. However, since the rubber content of the
hose wall under the strong compression band of the swaged ferrule tends to be displaced (rubber is not
compressible), it is therefore necessary to provide an escape area for this displacement. The ferrule
holes provide a portion of this and thus permit a tighter compression band. At the same time, we use this
rubber displacement to enhance the holding power of the coupling. The serrations (if present depending
upon style) are located under the compression band (swaged area) of the ferrule and act as “teeth”
biting into the hose cover.
3. Upon completion of the swage, the holes serve still another function. By visual inspection of the coupling,
the holes provide an indication of the adequacy of the swage. Rubber will normally project through the
bottom (inboard) row of holes (when present) and at least flow into the holes in the top (outboard) reservoir
area. The reservoir area should fill up (except when hose wall thickness is below 5/16").
The contour or swaged form of the Holedall coupling provides additional holding power (coupling retention).
The design of the ram swaging dies effect a swaged form to the Holedall coupling in which it should
be noted that the ferrule is not swaged its entire length. With the draw type progressive swage, the Holedall
coupling utilizes a planned forward (outboard) cold flow of the rubber content of the hose wall into the reservoir
area of the coupling. The hose wall, which is confined between the coupling stem and the tubular ferrule, should
(with our type swage) only move forward (outboard). As this occurs, the hose wall tends to slightly thin out in the
area of the swage and to become heavier in the forward reservoir area. Thus, when a Holedall coupling is
swaged onto a hose much of the same result is accomplished that is effected when one slides a nut onto a
section of rigid tubing and then flares the tubing. The nut cannot slide past the flared end of tubing and likewise
the Holedall coupling cannot slide past the flared hose end.
The die reduction, which effects the penetration of the ferrule into the hose wall, may vary with hose wall
construction. A Holedall coupling may be applied to almost any type of hose construction style with excellent
results. The degree of die reduction or subsequent ferrule penetration into the hose wall is dependent upon a
number of variable conditions, including the compound nature and thickness of the tube, the compound nature
and thickness of the cover stock, and the material and construction design of the reinforcing members. Desirable
ferrule penetration into the hose wall is normally approximately 20% of the hose wall thickness, but
it will vary with
the construction of the hose wall. In order to effect the proper ferrule penetration into the hose wall and to provide
compression band to withstand the hoop stress, it is necessary to increase the gauge or thickness of the ferrule
wall. Generally as the hose wall thickens and hose size increases, the ferrule is made with an increased wall
thickness.