When selecting or replacing butterfly valves, many engineers and purchasers assume that wafer butterfly valves with the same nominal diameter (DN) are interchangeable. In reality, this assumption can lead to serious installation problems.
One of the most frequently overlooked differences is how the face-to-face dimension is defined. Although an EPDM/NBR rubber seated wafer butterfly valve and a PTFE lined wafer butterfly valve may share the same external wafer-style appearance, their published face-to-face dimensions are measured from different reference planes.
Understanding this structural difference is essential to prevent installation errors, PTFE lining damage, and leakage after commissioning.
The face-to-face dimension is the axial distance between the two sealing reference planes of a valve. It determines the installation space required between pipeline flanges and is one of the most important dimensions for valve replacement.
However, the measurement reference differs depending on the valve design.
For conventional EPDM or NBR rubber seated wafer butterfly valves, the face-to-face dimension is measured:
Metal Body Face → Metal Body Face
This measurement method complies with commonly accepted butterfly valve standards such as:
Because the metal body determines the installation width, published dimensions are always referenced from the metal faces.
Although a PTFE lined wafer butterfly valve has a similar wafer-style body, its face-to-face dimension is measured differently.
The published dimension is:
PTFE Sealing Face → PTFE Sealing Face
rather than
Metal Body Face → Metal Body Face
To achieve complete corrosion protection, the PTFE lining covers every wetted surface inside the valve.
Unlike rubber-seated valves, the PTFE liner extends slightly beyond both metal body faces, creating raised sealing lips.
During installation:
Therefore, manufacturers define the face-to-face dimension using the outer PTFE sealing surfaces instead of the metal body.
Important:
Although both valves are wafer-type butterfly valves with nearly identical external profiles, they use completely different measurement reference planes.
Ignoring this dimensional difference can create costly installation problems.
If the pipeline spacing was originally designed for a standard rubber-seated valve:
The opposite situation also causes problems.
Since the PTFE sealing lips are absent:
Even when two valves have the same DN size, they should never be considered directly interchangeable without verifying the dimensional drawings.
The distinction extends beyond face-to-face dimensions.
| EPDM/NBR Rubber Seated Valve | PTFE Lined Butterfly Valve |
|---|---|
| Elastic molded rubber seat | Rigid PTFE liner |
| Seat integrated with valve body | PTFE liner supported by silicone or elastomer energizer |
| Suitable for water and general industrial service | Designed for highly corrosive chemicals |
| Metal body determines installation width | PTFE sealing lips determine installation width |
Because PTFE is considerably less elastic than rubber, the valve body must be specially designed to support the lining while maintaining reliable sealing performance.
To avoid installation failures, always follow these practices:
Always verify the manufacturer's 2D dimensional drawing before replacing any butterfly valve.
Ask the valve manufacturer whether the published dimension is measured from:
When upgrading from a conventional butterfly valve to a PTFE lined butterfly valve for corrosive media:
The difference lies in the measurement reference. An EPDM or NBR rubber seated wafer butterfly valve measures its face-to-face dimension from metal body face to metal body face, while a PTFE lined butterfly valve measures from PTFE sealing face to PTFE sealing face. Because the PTFE lining extends beyond the metal body to create the sealing surface, the published dimensions are based on the protruding PTFE lips rather than the metal casting.
Not always. Even if both valves have the same nominal diameter (DN), their installation dimensions may differ due to the different face-to-face measurement references. Before replacement, always compare the manufacturer's dimensional drawings and verify the required flange spacing to avoid damaging the PTFE lining or causing leakage.
It depends on the available flange spacing. PTFE lined butterfly valves have protruding sealing faces that require proper compression during installation. If the existing pipeline was designed for a conventional rubber seated valve, additional clearance or pipe spool adjustment may be required. Always confirm installation dimensions before ordering.
The face-to-face dimension is the axial distance between the two sealing reference planes of a butterfly valve. It determines the installation width between pipeline flanges. Depending on the valve design, the reference planes may be the metal body faces or the sealing surfaces of the valve liner.
The PTFE liner extends beyond the metal body to provide a continuous corrosion-resistant sealing surface. During installation, the pipeline flanges compress these PTFE sealing lips to create a leak-tight seal while preventing corrosive media from contacting the metal valve body.
Excessive flange compression can damage the rigid PTFE sealing lips. Unlike rubber, PTFE has limited elasticity and may crack, deform, or experience permanent creep if compressed beyond its design limits. This can lead to sealing failure and medium leakage.
Because their sealing structures are fundamentally different. Rubber seated valves seal through an elastic rubber seat contained within the valve body, while PTFE lined valves rely on protruding PTFE sealing faces. Since the sealing surfaces are different, the face-to-face measurement reference must also be different.
Do not rely solely on the nominal diameter (DN). Compare the following specifications before replacement:
Verifying these parameters helps ensure proper installation and reliable sealing performance.
PTFE lined butterfly valves are widely used in industries handling highly corrosive fluids, including:
Their full PTFE lining provides excellent resistance to strong acids, strong alkalis, and many corrosive chemicals.
Before placing an order, engineers should verify:
Confirming these details before procurement can prevent installation delays, reduce modification costs, and ensure long-term sealing reliability.
Although EPDM/NBR wafer butterfly valves and PTFE lined wafer butterfly valves often appear nearly identical from the outside, their face-to-face dimensions are based on different reference planes.
Understanding this seemingly small distinction is essential for successful valve replacement and reliable pipeline sealing. Before ordering or installing a butterfly valve, always verify the manufacturer's dimensional drawings and confirm the face-to-face measurement reference. Doing so can help prevent installation difficulties, protect the PTFE lining from damage, and eliminate the risk of costly leakage or rework.
With over 15 years of manufacturing experience, ISO 9001 & CE certification, advanced production facilities, and global export expertise, Laux Valve provides reliable butterfly valve solutions supported by professional engineering and responsive customer service.
