Just after nine last Thursday night, Lao Zhang, the equipment officer on a wastewater treatment plant expansion in northern Jiangsu, sent us a WeChat message: a DN300 wafer butterfly valve was installed and pressure tested, but the flange joint was weeping. The gasket was replaced once and it still leaked — was the butterfly valve at fault? In the photo, the valve's rubber seat ring had a deep compression mark along its edge. In our years as an authorized SUFA distributor, we take calls like this several times a year — the butterfly valve itself is fine; the fault lies in how it was installed.

A Wafer Butterfly Valve Can't Be Installed Like a Flanged Gate Valve

The most common mistake on site is treating a wafer butterfly valve like an ordinary flanged valve: slip the valve between two flanges, torque down the four bolts straight away, then test. When it leaks, add gaskets, swap gaskets — and it leaks worse with every change.

A wafer butterfly valve seals through the contact between the rubber seat on the valve body and the flange sealing faces — it doesn't use a gasket. The correct sequence: tack-weld one flange for positioning, hang the butterfly valve in place with the centering bolts, close up the other flange, then tighten diagonally and evenly, rotating the disc as you go. Cranking everything down in one go with uneven corner loads skews the seat ring — the weeping starts right there.

Our advice: before installing a butterfly valve in a chamber, wipe the flange faces and the seat ring clean and check whether the ring has any permanent creases from transport. A seat ring with a crease will never seal, however carefully it's installed.

Valve Chambers Are Tight, and Disc Position Is the Danger Zone

Two more high-frequency traps inside valve chambers. First, the disc scarring the pipe bore: if the valve stops in a half-open position during placement, the rotating disc scrapes the inside lip of the opposing flange and damages the sealing surface on the spot. Close the valve fully before placing it, hang it on the centering bolts, and confirm the disc clears the bore before closing up the flanges. Second, operating clearance: for a gear-operated butterfly valve, the handwheel needs room for a full turn. If the chamber wall is less than a fist's width from the handwheel, every future operation starts with dismantling the guard.

Last autumn at a waterworks project, a butterfly valve went into a deep chamber with the handwheel flush against the wall; nobody could work on it, and extra money was spent fitting an extension stem. One more look at the drawings would have prevented the whole thing.

Before Dismantling the Valve, Check Three Things in Order

When a butterfly valve's flange joint weeps, check in order: first, whether the bolts were tightened diagonally and evenly and haven't loosened; second, whether the seat ring has been squeezed into an edge rollover or worn unevenly; third, whether the two flanges are parallel — take a feeler gauge around the joint, and if the misalignment exceeds tolerance, realign the valve. Pulling the flanges flat with bolt force alone will only destroy the seat ring.

If all three check out and it still weeps, then suspect the valve body. SUFA ships every butterfly valve with a factory test record — if the shipping documents match, the product itself can basically be ruled out. During selection, compare the structural differences across series against your conditions in the product center; if in doubt, send the media, pressure, and size via the contact us page — ask first, install second.

The butterfly valve is the cheapest shut-off valve in a water system — and the one most often installed "just quickly." A properly installed butterfly valve saves no ten minutes; one round of rework means cofferdams, water shutoffs, and cranes all over again.

For the next butterfly valve going into your chamber — will "tighten diagonally and evenly, disc closed for placement" be written into the work permit at the installation briefing?

Suzhou Akameng Automation Equipment Co., Ltd. · Officially Authorized SUFA Distributor (Authorization No. SFSQ-0036) · Tel 0512-66673578 (WeChat 15851489497)