Understanding Oversized Bore Mechanical Seals
When selecting a mechanical seal, confirming the correct bore size is just as important as choosing the right seal type and face combination. For many pumps, a standard bore will suffice. However, certain pump models and applications require an oversized bore. Misidentifying this detail can lead to incorrect orders, failed installations, and costly downtime.
This article explains what an oversized bore is, when it’s required, and how Paradigm Seals™ makes the selection process simple.
What Is an Oversized Bore?
The bore refers to the inside diameter of the stuffing box where the mechanical seal is installed. In most pumps, this dimension matches standard sizing. However, some pump manufacturers design pumps with oversized stuffing boxes that require a seal with a larger bore dimension to ensure proper fit and operation.
Why Oversized Bores Matter
From personal experience, this is one of the most common and costly mistakes in seal selection. I ran into it many times throughout my career, and it was one of the very first things I trained new seal salespeople on — and often one of the first mistakes they made as well.
ANSI pumps, which are the most common in industry, are frequently offered with oversized (large-bore) seal chamber options. There is no reliable way to determine which bore a pump has by looking at the nameplate or the manual alone. Even experienced seal specialists must measure the seal chamber to confirm the correct bore size.
Selecting the wrong bore size doesn’t mean the seal is wrong — it simply means the seal will not fit.
How to Identify an Oversized Bore
Check Pump Model & Manufacturer
Many common ANSI pump models (such as Goulds 3196) may use oversized bores in certain sizes. Always cross-reference with a sizing guide.Measure the Stuffing Box
Using calipers, measure the internal diameter of the stuffing box. Compare this against standard bore specifications.Use Paradigm Resources
Paradigm Seals™ provides:An Oversized Bore Worksheet (PDF)
The online Find Your Seal Form for confirmation
Ordering Oversized Bore Seals from Paradigm Seals™
Paradigm Seals™ offers oversized bore options across our product families, including:
A1 Single Cartridge Seal — Oversized bore available in select sizes
A2 Dual Cartridge Seal — Oversized options for critical pumps
QuickCore™ Seals — Compatible with both standard and oversized bores
When placing an order online, simply choose “Large Bore” from the bore size dropdown to ensure the correct seal.
Key Takeaway
An large bore isn’t an uncommon complication—it’s a standard variation that pump operators must account for when ordering seals. By confirming manufacturer, model, and bore dimensions, you’ll avoid costly mistakes and downtime.
Paradigm Seals™ simplifies this process with clear sizing resources, an online selector tool, and knowledgeable support—helping you order with confidence.
Next Step:
Watch our full Oversized Bore Video Tutorial (below) for a step-by-step guide to identifying and ordering oversized bore seals.
Download the Stuffing Box Bore Sizing Worksheet (PDF)
