Mechanical Packers Overview Part 2 - Diameter

Mechanical Packer diameter is relevant for two reasons, 1) this dictates the size of the drill hole required, and 2) the overall surface area of the rubber in the drill hole is a key contributor to the pressure tolerance of a mechanical packer. 

1. Size of drill hole considerations: Industry standards require 45-degree drilling to insert mechanical packers to a crack depth that is ½ the thickness of substrate.  For thin substrates, for example 6” thick slabs, drilling at a 45-degree angle with a 5/8” drill bit may cause spalling and damage to the surface above the drilled angle as the outward heave force from the passage of the drill is greater than the strength of the concrete at that location, resulting in concrete spall and cracking damage at that location.  For these applications, Alchemy-Spetec offers 5/16” (8mm) and 3/8” (10mm) diameter packers (see FIGURE 1).  

   The smaller cross section of drilling produces much less heave force against the face of the concrete and offers much better results when drilling into a thin concrete substrate. 

   Post-tension structures and/or structures with a significant amount of rebar also present an obstacle when drilling.  By reducing the size of the drill bit by 40-50%, the contractor also decreases the probability of drilling into rebar or post-tensioning accordingly.

2. The tradeoff for smaller diameter is a decrease in pressure tolerances.  Common ½” (13mm) or 5/8” (16mm) mechanical packers tolerate spikes in pressure greater than 4,000psi (see FIGURE 2).  At 4,000psi, packers and ports can present a significant job-site hazard as they can exit the drill hole at dangerous velocities.  While injecting at these pressures are never recommended, a ½” (13mm) or 5/8” (16mm) rubber base on the mechanical packer will prevent blow-out significantly better than the 5/16” (8mm) or 3/8” (10mm) counterpart.