Guide
Well Seals 101: How to Choose, Size, and Maintain the Right Well Seal
A step‑by‑step guide to understanding well seals—what they are, how to size one correctly, and when to pick ABS vs. cast iron—plus installation tips and maintenance best practices.
What is a well seal?
A well seal is a two‑piece plate with a compressible gasket that clamps to the top of the well casing. It creates a sanitary barrier, supports the drop pipe and electrical wiring, and helps block insects, debris, and surface water from entering the well.
Most residential systems use 4 in., 5 in., or 6 in. casing sizes; commercial installs may be larger. Seals are available in multiple drop‑pipe bores and with one or more cord pass‑throughs.
How a well seal works
- Upper & lower plates sandwich a rubber gasket.
- Compression bolts draw the plates together, expanding the gasket against the casing ID.
- Center bore fits the drop pipe; pass‑throughs route cable and safety rope.
- Optional vent equalizes pressure while screening out insects.
ABS vs. cast iron well seals
| Feature | ABS (Thermoplastic) | Cast Iron |
|---|---|---|
| Strength | Good for most residential loads | Excellent—suited for heavier loads |
| Corrosion resistance | Non‑corroding; great in damp environments | Coated; long‑lasting when maintained |
| Weight | Light; easier to handle | Heavier; very durable feel |
| Cost | Typically lower | Typically higher |
| Best for | Standard residential installs | Demanding or commercial installs |
Not sure which to choose? Our team can help match the seal to your pump weight, setting depth, and code requirements.
Sizing a well seal in 3 steps
- Confirm casing size: Identify your well casing size by its outside diameter (e.g., 4", 5", 6"). The seal will state the casing size it fits.
- Match the drop pipe: Choose the center bore that matches your drop pipe (e.g., 1", 1‑1/4").
- Count the pass‑throughs: Ensure there are enough openings for power cable, safety rope, and any control wires; add a vent when required by local code.
Quick selection checklist
- Casing size matches well (OD)
- Center bore matches drop pipe
- Enough cable/rope pass‑throughs
- Vented when required by code
- Material: ABS for standard / Cast Iron for heavy‑duty
- Compatible with pitless adapter or cap arrangement
Common sizing & install mistakes
- Confusing casing ID and OD—always size the seal to casing OD.
- Forgetting venting when local code requires it.
- Under‑estimating load with deep settings and safety rope.
- Over‑tightening compression bolts; seat the gasket evenly.
Maintenance tips
- Inspect the seal when the pump is serviced; replace cracked gaskets.
- Ensure the vent screen is intact and free of debris.
- Re‑torque bolts evenly after temperature swings or service.
When to replace
Replace your well seal if you see gasket deterioration, rust‑through (on older cast iron), missing hardware, or persistent insect intrusion.
Find a replacement well sealFAQs
What does a well seal do?
It creates a sanitary barrier at the top of the well casing while supporting the drop pipe, wiring, and safety rope.
How do I size a well seal?
Match the seal to your casing outside diameter and drop pipe size, then check pass‑throughs and venting.
ABS vs. cast iron—how should I decide?
ABS is light and corrosion‑proof for typical homes; cast iron is heavier duty for higher loads or commercial systems.
Do I need a vented seal?
Often, yes—local codes may require it to equalize pressure and protect water quality. Always confirm your local requirements.
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