Translated from English
How can the space between your pipe and the opening in the wall of a chamber, tank, basin or concrete slab—where a hole has just been cut to allow the pipe to pass—be effectively and permanently sealed? This is the question we aim to address in the following pages. We present the available technology, as well as the combinations of specialised materials with mechanical fastening elements, to ensure a long-term, safe and reliable installation of various components.
Initially developed to seal and dampen vibration in hydraulic hoses installed in steel housings, modular mechanical sealing systems are now used to permanently seal and protect pipes passing through concrete walls, floors, ceilings and other barriers. They can be used for sealing grey or ductile iron, cement-based, metallic or plastic pipes against the openings they traverse, for pipes up to 144 inches (3650 mm) in diameter, ensuring hydrostatic sealing up to 5 bar.
These devices are installed around the external circumference of the pipe, a process that is faster and more efficient than conventional methods such as caulking with hemp and lead, prefabricated sealing rings type A or B, injected mastics or protective bellows (Figure 1).
When the bolts are tightened, the modular chain expands, filling the annular space between the pipe and the penetration opening, whether drilled, cast-in or formed. The annular space is defined as half the difference between the internal diameter of the penetration and the external diameter of the pipe.
The modular mechanical sealing devices consist of five components: an elastomeric sealing element (seal link), two pressure plates and a bolt/nut assembly. The sealing element (Figure 2) is typically manufactured from virgin EPDM (ethylene-propylene-diene monomer) rubber with a Shore A hardness of 50 ± 5 percent.
Thin seals for pipe and wall penetrations are manufactured from softer EPDM with a Shore A hardness of 40 ± 5 percent. This softer formulation allows sealing at lower torque, preventing deformation of the pipe. Other versions include nitrile rubber for enhanced resistance to oils, fuels and solvents, as well as silicone rubber for high-temperature applications or steam lines.
The elastomer formulation and geometric dimensions of the sealing element are engineered to ensure a uniform, smooth volumetric expansion. Virgin rubber ensures consistent vulcanisation, resulting in a solid expandable unit.
Because seals are supplied as a chain of links, it is essential that the hardness of these segments is nearly identical for the same size range, regardless of production batch. For example, if elements from different batches with different hardness values are combined in a single penetration, even when identical torque is applied to each joint, the elements will not expand uniformly, and the seal may be compromised.
Each sealing element includes two through-holes for the bolts, one on each side, with conical geometry so that tightening causes the material to compress securely around the bolt.
A moulded compression-assisting ridge on each side of the pressure plate allows increased compression load while preventing liquid ingress into cavities, optimising corrosion control (Figure 3).
The rubber volume around each bolt cavity must be precise to prevent bolt tear-through or loss of sealing during tightening.
Originally, modular mechanical devices employed pressure plates made from a combination of steel plate and PVC (Figure 4).
The bolt was threaded through the steel plates, while the applied torque and forces were distributed through the PVC housing. Field observations showed that PVC was unsuitable, being susceptible to cracking and to residual shrinkage around the steel insert, leading to seal loosening over time.
A finite-element analysis study conducted by the University of Michigan resulted in the replacement of the PVC/steel-insert pressure plates with plates made from a reinforced-nylon composite. By using moulded ribs, the redesigned pressure plates distribute forces more uniformly, offer higher dielectric strength, and improve corrosion resistance.
Bolt / Nut Combinations
Various bolt/nut combinations have been used over the years, from cadmium-plated carbon steel to today’s more advanced zinc-dichromate double-layer coatings in accordance with ASTM B-663, topped with a specialised lubricating layer for superior corrosion resistance. To test corrosion performance, four bolts were continuously submerged in tap water for four years, with results shown in Figure 5.
Bolt A is cadmium-plated carbon steel, B is cadmium-plated carbon steel with an anti-corrosion coating, C is double-layer zinc-dichromate carbon steel with an organic corrosion-resistant coating, and D is Type 316 stainless steel. Note the increasing corrosion resistance from bolt A to bolt D. Additionally, modular seals using bolts with organic anti-corrosion coatings over zinc-dichromate sub-coatings have withstood 1,470 hours of salt-spray testing per ASTM B117-97 without significant corrosion.
The differences between bolt diameter and bolt-cavity diameter are minimal, ensuring that the rubber sealing element expands primarily to fill the annular space between the pipe and the wall opening, rather than between the bolt and its cavity. Bolts—especially Type 316 stainless steel—are lubricated with PTFE-based compounds to prevent galling during tightening. On most modular seals, the nut applies torque to the pressure plates through two distribution planes (Figure 6).
Modular mechanical seals must be installed so that no leakage path is created through the penetration.
As noted, seals are supplied as belts or chains of elements, sized to provide the correct number of links for a specific application. These belts are tightened for shipping to ensure no components are lost. The belt must then be loosened to ensure that all gaps between individual sealing elements are fully closed (Figure 7).
Failure to close the gaps may create a path or space for liquid to pass through the seal.
The horizontal centreline of each pressure plate must align tangentially with the pipe so that torque from the bolt tightening is uniformly distributed into the sealing element. The pipe axis must be parallel to the penetration axis and centred within the opening. Pipes must be properly supported at both ends, as modular seals are not designed to carry pipe loads.
After linking the seal chain around the pipe, all bolt extensions protruding from the pressure plates must be of equal length to ensure uniform tightening. All pipe and penetration surfaces must be clean and free from dust, laitance, and casting defects. Any weld spatter in the sealing footprint must be removed as per the pipe manufacturer’s recommendations before installation.
After inserting the seal around the pipe, a loose or non-circular appearance is normal. Some installers may be tempted to remove what appears to be an “extra” link to make the seal slide more easily into the penetration. However, modular seal assemblies are supplied with the exact number of elements required for the penetration size. Removing links alters the volume-to-gap relationship and negatively affects performance. Smaller pipe diameters may require the links to stretch slightly. Pressure plates must be aligned so that their outer surfaces lie in the same vertical plane.
Penetration Opening Formation
While selecting and installing the correct seal is essential, proper formation of the penetration is equally important. Holes in cast concrete walls may be cored or formed using embedded sleeves made of steel, fibre-reinforced concrete, or thermoplastics. If cored, the opening must be free of casting defects, segregations, voids and debris. A modular seal can be installed directly in a cored hole. Minor defects can be repaired with epoxy resurfacing compounds.
If a steel sleeve is used, its external diameter must include a 50 mm circumferential flange for anchorage in the concrete wall and to prevent water migration around the sleeve. The flange should be continuously welded on both sides to ensure water cannot bypass it. The sleeve must be circular, clean and free from welding slag (Figure 8).
Fibre-reinforced cement sleeves are chemically compatible with concrete and include anchoring channels and hydraulic barriers for improved adhesion. Internal diameters range from 80 to 1200 mm, lengths from 200 to 1200 mm. They are tested at 5 bar differential pressure (Figure 9).
PVC sleeves feature textured surfaces for better bonding to concrete. The sleeve must withstand the forces exerted during concrete placement without deformation. Reinforced moulded ends assist positioning and maintain concentricity (Figure 10).
EqualIt is essential to maintain equal tightening force around the pipe. Seals must be tightened in a clockwise sequence, with no bolt turned more than two full turns per pass.
The seal is correctly sized when both the minimum and maximum pipe diameters fall within the published range. If incorrectly sized, the seal may slip or eventually be forced out of the penetration.
All modular seals allow for angular deviation, which depends on the relationship between the annular gap and the seal’s expansion range. The closer the annular space is to the centre of the expansion range, and the thicker the seal, the more misalignment can be tolerated. If pipe misalignment is expected by design, oversized sleeves or larger cored holes should be considered. Modular seals also provide limited vibration damping when pipe movement falls within allowable limits.
EPDM sealing elements used in heating, ventilation and air-conditioning applications exhibit a compression set of approximately 15% of their expansion range (based on exposure at 158°F / 70°C for 22 hours).
The smaller the seal, the smaller the expansion range, limiting reusability.
Modular mechanical seals have evolved substantially since their development over 45 years ago. Available tools now include a manufacturer-provided selection and calculation program to determine the optimal seal type and number of elements required for a specific penetration and vibration-damping needs. Bolts and pressure plates have been standardised, with small-size seal bolts redesigned from hex-head to Allen-head to facilitate installation in confined angular spaces. Additionally, redesigned pressure plates now provide up to 15% greater strength (Figure 11).
Properly designed and installed modular mechanical seals offer one of the safest, most cost-effective and reliable methods for sealing pipes and conduits passing through chamber walls, pumping stations, wastewater treatment basins, or concrete slabs. Numerous suppliers exist for these seals, though some still rely on technology dating back to the 1980s.
Ultimately, it is the responsibility of the specialist to select the materials most appropriate for the pipe and conduit penetrations, and the sealing system that best meets the requirements of the specific project.