Centrifugal, piston, gear, and diaphragm pumps all share one weak point: the flange joint between housing halves, where a single micron of gasket creep can turn into a steady drip under system pressure.

The Sealing Challenge

Pump housing flanges run continuously under high internal pressure or vacuum while the rotating assembly transmits constant vibration into the joint. Operating temperatures swing as the fluid — water, process chemicals, or oil — cycles through the system, and maintenance crews frequently work on aluminum or cast iron casings that were never machined to a mirror finish.

A cut gasket compresses once and then begins to relax; every thermal cycle after that first torque-down gives the joint a chance to creep, weep, and eventually fail outright.

Choosing the Right Anaerobic Sealant Chemistry

For this class of joint, a flexible, general-purpose anaerobic gasket sealant is the more forgiving chemistry. It cures only in the absence of air, between two clamped metal surfaces, so any material squeezed toward the pump’s wetted side stays uncured and inert rather than breaking into rubbery debris. Once fully cured it fills gaps up to roughly 0.5 mm, which matters on older or lightly pitted cast iron and aluminum castings, and it stays flexible enough to absorb the mechanical shock transmitted from rotating impellers and shafts without cracking. That same flexibility keeps internal components — bearings, shaft seals, impellers — in consistent alignment long after installation, because the cured film resists the slow “creep” that eventually loosens bolted joints sealed with compressible gasket material.

Getting the chemistry right also means accounting for how CTE mismatch drives adhesive bond failure between dissimilar metals in the joint, since a housing and its cover rarely share the same coefficient of thermal expansion — a mismatch that shows up as recurring seal failure long before anyone suspects the sealant itself. For a chemistry recommendation specific to your equipment’s materials and operating envelope, Email Us to reach our applications team.

Application Steps for a Reliable Seal

1. Preparation: Clean both flange surfaces thoroughly, removing all fluid residue, old sealant, and gasket fragments. An industrial-grade solvent such as acetone works well; the metal must be completely dry before application.
2. Application: Apply a continuous, even bead around the entire flange face, circling every bolt hole, then spread it into a thin, uniform film with a spatula rather than leaving a thick ridge.
3. Assembly: Mate the housing sections within about five minutes of application and torque the bolts to the pump manufacturer’s specification in the correct sequence.
4. Curing: Allow a full 24 hours before pressurizing the pump or introducing fluid, giving the sealant time to reach its working chemical and mechanical resistance.

Avoiding the Most Common Field Failures

Most field failures on a flexible anaerobic seal trace back to two causes: an over-thick bead, which slows the cure and leaves a soft, uncured core prone to blowout under vibration, or reusing a flange that still carries trace oil film from a previous seal. Since anaerobic chemistry cures by contact with active metal ions and the absence of air, even a light film of residual oil can leave sections of the pump housing flange under-cured.

Common Questions About This Application

Q: Is a cut gasket ever preferable to an anaerobic sealant here?

A: For a pump housing flange with wide, uneven, or previously damaged surfaces, a thicker gap-filling gasket can sometimes be justified, but it trades away the vibration resistance and long-term chemical stability an anaerobic sealant provides.

Q: Does the sealant need a chemical activator to cure properly?

A: On most ferrous and previously-sealed surfaces, ambient metal ions are sufficient to trigger the cure. A primer is worth adding only when the pump housing flange surface is unusually inert or was recently passivated.

Q: How thick should the bead be on a large, uneven flange?

A: Thick enough to bridge the widest gap on the pump housing flange, but no thicker — an oversized bead slows the cure disproportionately and increases the risk of squeeze-out into the fluid cavity.

Storage and Handling

Anaerobic sealants have a finite shelf life even unopened, since the same oxygen exposure that keeps them liquid in the bottle also slowly degrades the cure package over many months. Store cartridges upright, capped tightly, and away from direct heat or sunlight, and avoid letting the dispensing tip contact bare metal between uses — contamination at the nozzle is a common, avoidable cause of a partial cure on the next application to a pump housing flange.

Keeping the Seal Reliable Long-Term

A pump that leaks at the flange rarely fails all at once — it degrades quietly until an unplanned shutdown forces the issue. Choosing a sealant chemistry suited to vibration and imperfect cast surfaces, rather than defaulting to whatever gasket is on the shelf, is the difference between a five-minute rebuild and a repeat failure six months later. For a closer look at related bonding chemistry, see which UV glue delivers higher bond strength.

If your application calls for a sealant engineered to a specific pressure, temperature, or chemical-resistance profile, Contact Our Team to discuss the right formulation for your equipment.

Visit www.incurelab.com for more information.