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Every pipe that enters a precast concrete manhole or structure needs a watertight connection at the wall. Two families of resilient connector do that job: compression connectors and boot connectors. A-LOK Products, Inc. has manufactured both since 1971 in Tullytown, Pennsylvania. This explainer covers what each type is, how it seals, the A-LOK connectors in each family, and how to pick between them.
What a pipe to manhole connector does
A pipe to manhole connector is the resilient rubber component that seals the opening where a pipe passes through the wall of a precast structure. It has to hold a watertight seal while the pipe and the structure settle and move independently, and it has to do that for the life of the system.
Both create a watertight seal where a pipe enters a precast structure. A compression connector such as A-LOK PREMIUM seals by compression between the pipe and the connector cast into the structure wall. A boot connector is a flexible rubber sleeve secured to the pipe with a stainless steel clamp or band.
Compression connectors
A compression connector is a pipe to manhole connector that is cast directly into the precast structure, requiring no coring and producing no residual waste.
How it seals, in A-LOK’s words for the PREMIUM connector:
Functions on pure compression. After the pipe is beveled and the connector and pipe are cleaned and lubricated, the pipe is simply centered in the connector and inserted. Backfilling can be done immediately, thus enhancing project safety and overcoming the typical problems of water, running sand and other unstable trench conditions.
The A-LOK compression connector line
Four connectors, each with its own sizing range:
A-LOK PREMIUM
- Covered by the A-LOK Guarantee
- Viscoelastic Core Changes Shape With the Pipe
- Fits Existing Equipment
- Available for 12” to 102” OD Pipe
A-LOK X-CEL
- Covered by the A-LOK Guarantee
- Patented “Water Pocket” Energized by Hydrostatic Pressure
- Available for 4 ¼” to 102″ OD Pipe
A-LOK STM
- Economical Connector for Stormwater Applications
- Accommodates Round and Elliptical Pipes
- Available for 8” to 102” OD Pipe
INSERTA-LOK
- Ideal Choice for Cored or Cast Openings
- Tapered Profile Enhances Coupling Characteristics
- Available for 4” to 13” OD Pipe
Compression connectors are sized to the pipe’s actual outside diameter, not its stated size, because the connector seals against the outside of the pipe. See the Dimensional Data page and the How to Order guide.
Boot connectors
A manhole boot connector is a flexible rubber boot for sealing pipe to manhole and precast structure entries, producing a positive watertight seal between the pipe and the structure. A-LOK Products, Inc. manufactures four boot connector lines: QUIK-LOK, Z-LOK, Z-LOK STM, and the G3 BOOT SYSTEM, covering sanitary and stormwater systems and pipe sizes from small laterals up to 65 inch large diameter pipe.
The A-LOK boot connector line
Each boot is described in full in the boot connectors guide. The short version, in the guide’s own words:
QUIK-LOK
The stainless steel takedown clamp is manufactured as an integral part of the rubber connector. Up to 20 degrees of omnidirectional deflection and 1.00 inch of vertical or horizontal movement.
Z-LOK
Z-LOK provides up to 25 degrees of omnidirectional deflection and 1.50 inches of vertical or horizontal movement without loss of seal, the most flexibility in the A-LOK boot line.
Z-LOK STM
The Z-LOK STM connector was designed by A-LOK Products, Inc. to address the need for a boot style connector for large diameter pipe, and it is available for 13 inch to 65 inch pipes. Z-LOK STM is suited for applications using either smooth wall pipe or corrugated pipe with an oversleeve.
G3 BOOT SYSTEM
The G3 BOOT SYSTEM works for sanitary or stormwater systems. The G3 Boot System withstands 15 degrees of omnidirectional deflection and one half inch of centerline offset while maintaining a watertight connection.
| Boot | Omnidirectional deflection | Vertical or horizontal movement |
|---|---|---|
| QUIK-LOK | Up to 20 degrees | 1.00 inch |
| Z-LOK | Up to 25 degrees | 1.50 inches |
| Z-LOK STM | Up to 10 degrees | 1.50 inches |
| G3 BOOT SYSTEM | 15 degrees | One half inch of centerline offset |
How the opening is made matters too
Precasters create the pipe opening in one of three ways: cast in at the plant with a mandrel (a formed opening), cored after casting, or scored and knocked out in the field. Compression connectors and cast-in boots go in with the mandrel at the plant. INSERTA-LOK is the ideal choice for cored or cast openings. QUIK-LOK can be installed into concrete structures in the plant, or with a field sleeve for cast-in-place at the job site. A-LOK’s Installing and Verifying A-LOK Compression Connectors guide covers the mandrel work and the post-pour checks.
Compression vs. Boot Connectors: How to Choose
When evaluating structure-to-pipe connections, both options have their place, but compression gaskets offer distinct advantages in speed, efficiency, structure sizing, and long-term durability.
Here is how to choose the right connector based on five primary jobsite questions:
1. What structure size do you need?
- Compression: Maximize pipe capacity while minimizing structure size. Because the gasket profile is cast into the curved wall geometry, you can fit larger pipes into smaller, lower-cost structures.
- Boot: Requires a flat, straight plane for the take-up clamp to tighten properly. This constraint limits the maximum pipe size you can install in a given structure.
2. What are the jobsite labor and trench safety requirements?
- Compression: Streamlines installation and maximizes worker safety. With zero field clamping required, crew members simply lubricate and home the pipe, allowing immediate backfilling and dramatically reducing time spent in open excavations.
- Boot: Requires workers to manually enter the trench to align the stainless steel take-up clamp and torque it down to the required manufacturer specifications, adding installation steps and extending trench exposure time.
3. Are there corrosive soils or aggressive site environments?
- Compression: Built for maximum long-term reliability. Its all-rubber sealing surface contains zero exposed metal components, eliminating corrosion risks from soils, chlorides, or runoff over decades underground.
- Boot: Relies on external stainless steel band clamps (typically 305 or 316 grade). While durable, these metal components require extra evaluation when installed in highly acidic soils, high-chloride areas, or aggressive chemical environments.
4. What is the pipe material and outside diameter (OD)?
- Compression: Provides a seamless, reliable seal with precise radial tolerances when working with standard, smooth-wall pipes (PVC, concrete, ductile iron, and smooth-wall HDPE).
- Boot: Offers flexible field adjustment for non-standard wall thicknesses, wider OD variations, or corrugated exterior pipe profiles.
5. What ground movement, pipe slope, or differential settlement is expected?
- Compression: Offers engineered omnidirectional deflection that reliably handles standard settlement, ground movement, and typical slope transitions in stable, standard soil conditions.
- Boot: Provides extended angular deflection and higher shear displacement in extreme conditions like uncompacted soils, severe slopes, or high-settlement fill areas.
Frequently asked questions
What are the two main types of precast manhole connectors?
Compression connectors, which are cast into the structure wall and seal by compression against the pipe, and boot connectors, which are flexible rubber sleeves secured to the pipe with a stainless steel clamp or band.
What is a cast-in connector?
A connector cast directly into the precast structure at the plant, requiring no coring and producing no residual waste. A-LOK PREMIUM, A-LOK X-CEL and A-LOK STM are compression connectors; Z-LOK is a cast-in boot.
Which A-LOK connectors are for stormwater?
A-LOK STM on the compression side and Z-LOK STM on the boot side are designed for stormwater. The G3 BOOT SYSTEM works for sanitary or stormwater systems, and A-LOK PREMIUM, A-LOK X-CEL, QUIK-LOK and Z-LOK are listed for ASTM C1478 as well as C923.
What pipe sizes do A-LOK connectors cover?
Compression connectors from 4″ OD (INSERTA-LOK) up to 102″ OD (A-LOK PREMIUM, A-LOK X-CEL, A-LOK STM). Boot connectors from small laterals up to 65 inch large diameter pipe (Z-LOK STM).
How do I order the right connector?
By the pipe’s actual outside diameter and pipe manufacturer, not its stated size, matched to the connector and mandrel part numbers on the dimensional data sheet. The How to Order guide walks through it, and A-LOK confirms sizing before anything ships.
Not sure which connector fits the job?
Tell us the pipe, the structure and the specification and we will point you to the right one.