Expansion plugs provide a permanent, leak-tight sealing of fluid passages in hydraulic manifolds, castings, and other components without having to use O-rings, threads, or sealants. Several methods exist for installing the plug and expanding its circumference to establish as tight seal against the inside diameter of the drilled hole.
Ball style—Originally developed as an alternative to threaded plugs, ball style expansion plugs simplified the machining of the end of the drilled hole. The plug’s design uses a simple +0.12/−0.00 mm) counterbore hole to ensure a permanent, leak-proof seal, at pressures to 6,250 psi (350 bar) at a 3:1 safety factor.
Installation for low-volume applications is accomplished using a set tool and hammer or an arbor press, tapping or pressing the ball down into the sleeve until reaching its final desired position. In higher-volume applications, operators air hammers or automate equipment is used to drive the ball into the sleeve, thus speeding up the installation.
Rivet style—developed about 30 years ago, rivet-style plugs again simplified machining of the end of the drilled hole, requiring only a straight bore (+.12 mm/−0). The design often requires a smaller plug being than with the ball style. Rivet-style plugs introduced a hydro-pneumatic installation tool to secure the proper installation of the expander, virtually eliminating any potential installation error by relying on the tool to break the plug vs. an operator pressing the ball to the proper depth.
Operators insert the plug into the hydro-pneumatic tool, press the plug against the hole to be sealed, and depress the tool’s trigger. With the tool maintaining flush contact with the surface of work piece, the internal components of the tool grab a mandrel while holding the body of the plug just below the surface of the workpiece. The tool draws the pin into the body until the necked down area of the plug reaches its desired break point. When this occurs, the pin fully engages the body, causing radial expansion sealing the hole at 7,250 psi (500 bar) at a 3:1 safety factor. A quick, simple, and cost-effective permanent seal, the rivet style plug was an improvement to expansion plugs for many applications.
A Newer Option
These two options come in a variety of material choices, sizes, pressure ratings, and installation tools. The EIS pull plug was introduced in 2013 and automatically threads the plug onto the installation tool’s mandrel until ready to insert into the hole for sealing. Unlike the ball-style plus, the EIS Pull Plug does not require a counterbore, nor does it rely on the reaching a break force, as with the rivet-style plug
Read more: Expansion Plugs Provide Leak-Tight Sealing of Fluid Channels