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    Weir Type Diaphragm Valves sourcing

    About Weir Type Diaphragm Valves

    Weir type diaphragm valves in cast iron, WCB, CF8M and rubber or PTFE lined bodies, DN15 to DN350, for corrosive, abrasive and throttling duties.

    A weir type diaphragm valve closes a flexible elastomer or PTFE-faced diaphragm against a raised saddle, or weir, cast into the valve body. Because the diaphragm travels only a short distance to reach the weir, it flexes less per cycle than a straight-through diaphragm, lasts longer, and gives usable throttling in the mid-travel range. The diaphragm also isolates the bonnet and working parts completely from the line fluid, which is why the design dominates corrosive chemical, demineralised water, effluent and mild slurry services. Indian manufacturers commonly supply bodies in cast iron, WCB carbon steel and ASTM A351 CF8M stainless, with linings in natural rubber, neoprene, EPDM, butyl and PTFE or PFA for aggressive acids, and diaphragms in the matching elastomer grades or PTFE with an elastomer backing. Typical sizes run DN15 to DN350 at PN10 or PN16, flanged to ASME B16.5 Class 150 or EN 1092, with screwed ends on small bores. An enquiry should state size, body material, lining, diaphragm grade, the medium with concentration and temperature, working pressure including any vacuum, end connections and quantity.

    Buyer guide

    Specifying Weir Type Diaphragm Valves: Lining, Diaphragm, Rating and Duty

    01

    What the valve is actually for

    A weir type diaphragm valve isolates and throttles corrosive, abrasive or contamination-sensitive fluids by pressing a flexible diaphragm onto a weir cast across the flow passage. Nothing but the body lining and the diaphragm ever touches the fluid, so there is no gland to leak and no metal trim to corrode, which is why the design is the default in chemical dosing, water treatment, electroplating, fertiliser and effluent lines.

    02

    Body and lining choices

    Indian foundries commonly supply cast iron and WCB bodies with vulcanised linings in natural rubber, neoprene, EPDM, butyl and hypalon-type elastomers, unlined CF8M stainless bodies to ASTM A351 for cleaner services, and PTFE or PFA lined bodies for hot concentrated acids and solvents. The lining is the pressure-retaining wetted surface, so its bond quality and spark test matter as much as the casting.

    03

    Diaphragm materials

    The diaphragm normally matches or exceeds the lining chemistry: rubber grades for abrasive and dilute chemical duty, EPDM for hot water and oxidising media, and a PTFE face with an elastomer backer where permeation or aggressive chemistry rules elastomers out. Diaphragms are consumables; agree a spares quantity in the same order.

    04

    Sizes, ratings and ends

    Weir valves are commonly offered DN15 to DN350. Pressure ratings step down with size, typically around 10 bar on small bores falling to 3.5 to 6 bar on large bores, so check the manufacturer rating chart rather than assuming a flat PN16. Ends are flanged to ASME B16.5 Class 150 or EN 1092 PN10/16, with BSP or NPT screwed ends on small sizes.

    05

    Operation and options

    Handwheel operation with a position indicator is standard; specify an adjustable closing stop to protect the diaphragm from over-torque, a padlockable handwheel where isolation must be secured, and a sealed bonnet with leak-detection port on toxic duty. Bonnets convert to pneumatic actuation, so state any automation intent at enquiry. For vacuum service ask for a stud-backed diaphragm that is positively retracted.

    06

    Applicable standards

    Specify design to MSS SP-88 or EN 13397; BS 5156 remains a legacy reference in older specifications. Testing is offered to API 598 or the MSS SP-88 provisions.

    What to state in the enquiry

    Give size and quantity, body material and lining, diaphragm grade, medium with concentration and temperature, working pressure and any vacuum, end connections, handwheel or actuated operation, governing standard, inspection and export packing requirements. Complete data lets manufacturers quote correct linings first time instead of assuming.

    Submit an enquiry →
    Technical guide

    How Weir Type Diaphragm Valves Work

    The closing mechanism

    In a weir type diaphragm valve the flow passage rises over a saddle-shaped weir cast across the body. A flexible diaphragm, clamped between body and bonnet around its full perimeter, is pushed down by a shaped compressor until it moulds onto the weir crest and shuts off flow. Because the weir raises the seating line close to the diaphragm, the stroke is short, roughly a quarter of the bore, and the diaphragm bends through a small angle each cycle. That single geometric fact is why weir valves outlast straight-through valves on the same duty and why stiff PTFE-faced diaphragms, which cannot tolerate deep flexing, are practical only on weir bodies.

    Complete fluid isolation

    The diaphragm is both the closure member and the stem seal. The spindle, compressor and bonnet stay dry, so there is no packing to adjust and no emission path, and the fluid sees only lining and diaphragm. This is also why the valve suits contamination-sensitive duty in both directions: the process cannot reach the mechanism and the mechanism cannot shed metal or lubricant into the process.

    Flow behaviour and throttling

    Flow over the weir gives the valve a usable characteristic between about 20 and 80 percent open, where lift correlates reasonably with flow. Near the seat the elastomer deforms unpredictably and close to full open the extra lift adds little capacity, so weir valves make good manual regulating valves but are not precision control valves; where accurate modulation is needed a characterised control valve to IEC 60534 practice is the correct tool. The weir does add resistance, so pressure drop is higher than a full-bore pattern.

    How they fail

    Diaphragms fail by flex fatigue at the weir line, by chemical attack or permeation that swells and softens the elastomer, and by over-compression when operators keep tightening a handwheel onto an already-seated diaphragm. Vacuum service can pull an unsupported diaphragm away from the compressor unless it has a stud or bayonet fixing, so state vacuum in the enquiry. Lined bodies fail at lining holidays and bond defects, which is why reputable Indian manufacturers spark test linings before despatch.

    Why the details matter

    A closing travel stop protects the diaphragm from over-torque, a rising indicator shows position on non-rising handwheel designs, and a correctly matched diaphragm and lining pair turns a commodity valve into one that runs years between diaphragm changes. Diaphragm replacement itself needs only bonnet bolts and a spanner, one reason the type is favoured where maintenance windows are short.

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    Frequently Asked Questions

    Weir type or straight-through diaphragm valve, which should I specify?
    Which body lining should I choose for my medium?
    What standards apply to weir type diaphragm valves?
    What should my RFQ for weir diaphragm valves include?
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