DN300 U-Type Butterfly Valve with Hard Back Seat

SS304 Back-Up Ring | Anti-Extrusion Design | Higher Pressure & Vacuum Capability | PN16

Product Overview

The Laux Valve DN300 U-Type butterfly valve with hard back seat is an upgraded version of our standard U-Type butterfly valve. In this design, the rubber seat is backed by a stainless steel back-up ring (hard back seat), which mechanically supports the full circumference of the rubber liner. This hard support ring prevents the elastomer from cold-flowing, extruding, or distorting under pressure — a common failure mode of standard rubber-seated butterfly valves.

The hard back seat construction delivers three key benefits: (1) higher allowable pressure without seat extrusion, (2) reliable sealing under vacuum conditions, and (3) significantly extended seat life in high-cycle and high-pressure service. This makes the DN300 hard back seat U-Type valve the preferred choice for pump discharge lines, high-rise building supply systems, and industrial processes where standard rubber seats would fail prematurely.

What is a Hard Back Seat? Technical Explanation

A "hard back seat" (also called a back-up ring, seat support ring, or anti-extrusion ring) is a rigid metallic ring mounted behind the rubber seat in the body groove. In a standard U-Type butterfly valve, the rubber liner sits directly in the body groove and relies only on its own stiffness to resist pressure. Under high pressure, especially in large sizes like DN300, the rubber can deform, "cold-flow," or squeeze (extrude) into the flow passage — degrading the seal and shortening seat life.

The hard back seat eliminates this problem:

• Mechanical support — The SS304 back-up ring fully supports the rubber liner around its entire circumference, preventing deformation under pressure.
• Anti-extrusion barrier — The ring closes the gap between the rubber and the body groove, stopping the elastomer from squeezing into the bore.
• Vacuum stability — Under negative pressure (vacuum), the hard ring prevents the rubber from being sucked away from the disc, maintaining the seal.
• Dimension retention — The rigid ring maintains precise seat dimensions over the valve's life, ensuring consistent sealing geometry.

1. SS304 Back-Up Ring

The heart of the hard back seat design is a precision-formed SS304 stainless steel ring that sits in the body groove behind the rubber seat. The ring matches the exact contour of the rubber liner and is manufactured with tight dimensional tolerances to provide uniform support around the full 360-degree circumference.

• Material: SS304 (standard); SS316L available for corrosive media
• Thickness: 2-3 mm depending on pressure rating
• Profile: L-shaped or U-shaped section matching the rubber contour
• Corrosion resistance: No coating required — stainless steel is inherently corrosion-resistant

2. Bonded Rubber-to-Metal Construction

The rubber seat is vulcanized (bonded) onto the SS304 back-up ring, creating a single integrated seat assembly. This bonded construction has several advantages over loose ring designs:

• No relative movement between rubber and ring — no friction wear at the interface
• The ring cannot shift or rotate out of position during assembly or operation
• Replacement is a single-piece operation — remove old seat assembly, install new one

3. Dovetail Anchoring in Body

The complete seat assembly (rubber + ring) is anchored in the body's dovetail groove. The combination of the dovetail mechanical interlock and the hard ring's rigidity ensures the seat assembly cannot dislodge, even under surge pressures or water hammer.

4. Flange Gasket Function Maintained

Despite the added hard ring, the rubber liner still extends beyond the body faces to form the integral flange gaskets. No external gaskets are required, and the valve remains fully interchangeable with standard U-Type valves in the pipeline.

Key Features

• SS304 Hard Back-Up Ring — Rigid stainless steel ring bonded behind the rubber seat prevents cold flow, extrusion, and distortion under pressure and vacuum.
• Higher Pressure Capability — The hard back seat allows the DN300 valve to maintain bubble-tight sealing at full PN16 rating, including surge conditions, where standard seats would begin to extrude.
• Vacuum Service Approved — The rigid ring prevents the rubber from collapsing inward under vacuum, making the valve suitable for suction lines and vacuum systems down to 0.1 bar absolute.
• 2-3x Longer Seat Life — By eliminating rubber deformation as a failure mode, the hard back seat significantly extends service intervals in high-cycle and high-pressure applications.
• Replaceable Seat Assembly — The bonded rubber + ring assembly is field-replaceable in 1-2 hours without removing the valve from the pipeline.
• U-Type Body Design — U-shaped body cross-section provides high rigidity and full-face flange sealing with dead-end service capability.
• Bi-Directional Bubble-Tight Seal — Zero leakage in both flow directions per ISO 5208 Rate A.
• Worm Gearbox Standard — Self-locking worm gearbox with handwheel provides smooth operation and position holding.
• Blowout-Proof Stem — Anti-blowout stem with double O-ring sealing prevents external leakage.
• ISO 5211 Mounting — Standard mounting pad for pneumatic or electric actuator upgrade.

Technical Specifications

Applications

• Pump Discharge Lines — Where surge pressure and water hammer can destroy standard rubber seats
• High-Rise Water Supply — High static pressure zones in tall buildings (PN16 rated)
• Vacuum / Suction Systems — Pump suction, vacuum tank isolation, degassing lines (0.1 bar abs)
• Water Treatment & Distribution — Potable water mains, filter backwash, high-pressure zones
• Wastewater — High-pressure sludge and sewage lines where abrasion + pressure combine
• HVAC & District Heating — High-pressure chilled water and hot water systems
• Fire Protection — High-pressure fire mains and pump isolation
• Industrial Process — Cooling water, utility water, chemical dosing, compressed lines

Frequently Asked Questions

Q: What exactly is the "hard back seat" in this valve?

A: The hard back seat is a stainless steel (SS304) back-up ring that is vulcanized onto the back of the rubber seat. The ring sits in the body groove and fully supports the rubber liner around its entire circumference, preventing the rubber from cold-flowing or extruding under pressure. It effectively turns the soft rubber seat into a reinforced, dimensionally stable sealing element.

Q: How does the hard back seat improve pressure capability?

A: Standard rubber seats deform under high pressure because nothing supports them from behind. The rubber can squeeze into the flow passage (extrusion), breaking the seal. The hard back seat's rigid ring blocks this movement completely, so the DN300 valve maintains bubble-tight sealing at the full PN16 rating — including surge pressure conditions where standard seats would fail.

Q: Can this valve be used in vacuum service?

A: Yes. Under vacuum, the pressure differential pulls the rubber seat inward, away from the disc, which causes standard seats to leak or collapse. The SS304 back-up ring prevents this inward collapse, allowing reliable sealing down to 0.1 bar absolute (10 kPa). Each valve is vacuum tightness tested per EN 12266-1 before shipment.

Q: Does the hard back seat affect seat replacement?

A: No. The rubber seat and SS304 ring are bonded into a single seat assembly. Replacement is actually easier — you remove and install one integrated component, and the ring ensures the new seat positions itself correctly in the groove.

Q: How much more does the hard back seat version cost?

A: The hard back seat version costs approximately 15-25% more than the standard seat version. However, considering the 2-3x longer seat life and the ability to handle higher pressure and vacuum, the total cost of ownership is typically lower — especially in demanding applications.

Q: Can the hard back seat be supplied with other seat materials?

A: Yes. The SS304 back-up ring can be bonded with EPDM (standard), NBR, Hypalon, or Viton rubber to suit your media and temperature requirements. SS316L back-up ring is available for highly corrosive environments.

Q: Is this valve interchangeable with standard U-Type valves in the pipeline?

A: Yes. The hard back seat version has identical face-to-face dimensions, flange drilling, and body profile as our standard DN300 U-Type valve. It can be directly substituted in existing installations without piping changes.

Ordering Information

To order, please specify: size (DN300), pressure rating (PN16), seat material, back-up ring material (SS304/SS316L), disc material, operation type, and quantity. Contact our sales team for pricing and delivery.

Email: james@lauxvalve.com | Tel / WhatsApp: +86 18920833829

Laux Valve — Professional Butterfly Valve OEM Manufacturer Since 2011 | ISO 9001 & CE Certified | Factory Direct Pricing

Butterfly Valve Manufacturing Process
From Technical Confirmation to Final Delivery



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From raw material inspection to final delivery, every butterfly valve undergoes a comprehensive quality inspection to ensure reliable performance and compliance with international standards.

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