Flanged seal for rotary valves: types and installation

Wafer Seal for Butterfly Valves: Types, Design and Installation

Butterfly valves hold a firm position in piping systems thanks to their compactness, low weight and high operating speed. However, their leak‑tightness directly depends on the element located between the body and the pipeline flanges — the wafer seal. It is precisely this component that retains the working medium and determines the service life of the entire valve assembly. In this article we will look at the types of these seals, what they are made of and how to ensure long, trouble‑free operation.

1. Purpose and Role in a Butterfly Valve

A butterfly valve shuts off the flow by rotating a disc that, in the closed position, presses against the seat. The seat, in turn, performs a dual task: it seals the bore relative to the disc and the joint between the valve and the mating pipeline flanges. A design in which the seal is clamped between flanges is called a wafer design. The wafer seal of butterfly valves absorbs static pressure, temperature fluctuations and multiple deformations during every cycle. Its condition determines whether the valve will maintain leak‑tightness class A according to GOST 9544‑2015 after thousands of operations.

Butterfly valves with a seal of this type are mounted on pipelines with diameters from 40 to 1200 mm and above, operating at pressures up to 63 bar. With a seal made of modern elastomers or polymer composites, they are able to shut off not only water and air but also aggressive media, including acids, alkalis, oils and steam. The accuracy of seal centring during installation is critical: a shift of a couple of millimetres will lead to leaks and accelerated wear.

2. Design and Materials Used

A basic wafer seal is a ring whose shape exactly matches the profile of the valve body and the mating flanges. The sealing element is inserted into a groove in the body or, in some models, is directly clamped between the flanges. When the disc closes, the elastic material deforms, filling micro‑irregularities and creating a tight contact. The force required for compression depends on the hardness of the material and the profile shape; to reduce the operating torque, special coatings with a low coefficient of friction are often applied.

Materials are strictly selected for the working medium and the temperature range:

• Ethylene‑propylene‑diene rubber EPDM. Resistant to water, steam, air, weak acids and alkalis. Operating temperature from –30 to +130 °C. Not suitable for petroleum products, as it swells.
• Butadiene‑nitrile rubber NBR. Resistant to oils, petroleum, greases, diesel fuel. Temperature limit is about –20…+100 °C. Widely used in hydraulics and fuel systems.
• Fluoroelastomer FKM (Viton). Withstands high temperatures up to +200 °C, aggressive liquids, acids. Used in the chemical industry.
• Polytetrafluoroethylene PTFE (fluoroplastic). Exceptional chemical resistance, temperature range from –200 to +260 °C, low friction. Often used in combined constructions, since pure PTFE is prone to cold flow.

In addition to elastomers, the design may include metal rings of carbon or stainless steel, spring elements of alloys such as Inconel, and graphite fillers. Metal‑rubber and multi‑layer constructions withstand higher pressures and temperatures. The surface roughness of the flanges plays an important role: the lower it is, the thinner the seal can be and the higher the leak‑tightness.

3. Types of Wafer Seals

The variety of wafer seal types makes it possible to select a solution for specific operating conditions. Let us consider the main types, their arrangement and field of application.

3.1. Solid Rubber Seat

The simplest and most mass‑produced design. A ring of EPDM or NBR is formed by moulding and inserted into a groove in the valve body. When installed between the flanges, it is compressed and fixed. Such seals are typical for valves with a nominal pressure of PN 10–16. The service life in cold‑water supply systems reaches 15–20 years; however, under frequent cycles and elevated temperatures, the rubber hardens and cracks over time. Replacing a solid seat in some models requires removing the valve, which is why replaceable designs are gaining increasing popularity.

3.2. Replaceable Seat with a Metal Base

The elastomer is vulcanised onto a steel ring that provides rigidity and facilitates centring during installation. Such a seat can be replaced without dismantling the valve body. It is used at pressures up to 25 bar and temperatures up to 120 °C. The metal base prevents the seal from rotating when the flanges are tightened, which is especially important for automated valves with high torque. Several bolts on the body fix this ring, allowing repairs to be carried out in the field in a short time.

3.3. Disc‑type Wafer Seal

This is a multi‑layer construction in which flat elastic gaskets, steel rings and graphite inserts alternate. Due to the set of layers, high resistance to pressure and temperature fluctuations is achieved. Such seals are often chosen for shut‑off valves in heat supply networks and steam pipelines. They withstand flange misalignments of up to 1–2 degrees, which facilitates installation on pipelines with imperfect geometry. Detailed specifications for this type of product are given in the disc‑type wafer seal section.

3.4. Combined Wafer Seal

The most complex and reliable type. It combines polymer seats, spring metal rings, graphite and fluoroplastic inserts. This combination produces a self‑tightening effect under temperature cycling and compensates for wear. Combined seals are installed in critical sections in the power industry, petrochemistry and on superheated steam pipelines. Their distinctive ability is to maintain leak‑tightness during temperature fluctuations of hundreds of degrees, when ordinary elastomers have already lost their properties. Technical characteristics and available designs can be found on the combined wafer seal page.

4. Comparative Table of Seal Types

5. Installation and Replacement of a Wafer Seal

The installation of a wafer seal requires compliance with a number of rules. Before starting work, the flanges are thoroughly cleaned: remnants of the old seal, rust and burrs are removed. The flange face must be clean and dry. A straightedge and feeler gauge can be used to check flatness. If the flanges have dents or deep scratches, they are ground or restored by weld overlay followed by machining.

The procedure during installation:

1. Remove the preservative from the seal and check it for cracks, tears and foreign inclusions. If necessary, keep it at room temperature for at least 2 hours.
2. Place the seal in the groove of the valve body. If the design has no groove, position it strictly in the centre between the flanges, using centring rings or a template.
3. Insert the valve between the pipeline flanges, insert the bolts by hand, making sure that the seal has not shifted.
4. Tighten the bolts in a cross‑pattern in three or four passes, gradually increasing the torque to the nominal value specified by the manufacturer. Monitoring is carried out with a torque wrench. Insufficient torque will lead to leaks, excessive torque — to deformation and destruction of the seat.
5. After uniform tightening, turn the disc by hand: it should move smoothly, without jamming or jerks. At the slightest resistance, loosen the flanges and check the centring.
6. Carry out a hydraulic test at nominal pressure for at least 10 minutes, observing the joint. If a leak is detected, release the pressure, re‑tighten the bolts and repeat the test.

Replacement of a worn seal is carried out similarly, with mandatory cleaning of the seating surfaces. When changing from one seal type to another, the geometric dimensions and compatibility with the mating flanges are verified. Replaceable seats with a metal base are secured with additional anti‑rotation screws, which must be tightened with the same torque as the main bolts.

6. Causes of Wear and Diagnostic Methods

The service life of a wafer seal depends on a number of factors: the number of open‑close cycles, the abrasiveness of the medium, temperature, pressure and the quality of installation. The main wear mechanisms:

• Mechanical abrasion. The disc rubs against the seat during every actuation. In the presence of sand, rust or scale, wear accelerates. Abrasive particles act like emery paper, gradually cutting away the upper layer of the elastomer.
• Chemical degradation. An incorrectly chosen material swells, loses elasticity or breaks down. For example, EPDM in oil swells and ceases to perform its function after only a few days.
• Thermal ageing. At temperatures close to the upper limit, elastomers oxidise and become brittle. Cyclic temperature changes aggravate the process, especially if the material is not designed for such fluctuations.
• Incorrect tightening. Excessive force deforms the seal, while insufficient force leaves clearances. Uneven tightening causes local overheating and accelerated destruction.

Diagnostic signs of wear: the appearance of droplets on the body, an increase in the torque on the handle or actuator, noise when shutting off the flow, visible cracks on the edge of the seat during inspection. Regular visual inspections and a scheduled replacement plan every 5–7 years make it possible to avoid sudden failures. For critical sections, a log is kept in which the date of installation, the number of cycles and the results of inspections are recorded.

7. Applications in Various Industries

Wafer seals of butterfly valves are found everywhere:

• Water supply and sewerage. Valves with an EPDM seat shut off cold and drinking water mains. Leak‑tightness class A is mandatory. In sewer collectors, the seals come into contact with aggressive effluents, therefore chemically resistant grades are chosen.
• Heat supply networks. For hot water and steam up to 200 °C, metal‑rubber or disc‑type multi‑layer seals are used. They withstand temperature cycling without loss of elasticity, which is especially important during seasonal start‑up and shut‑down of boiler houses.
• Oil and gas sector. NBR seats operate on pipelines for light petroleum products. For media with hydrogen sulphide, special NBR grades with reduced gas permeability are used, complying with the NACE MR0175 standard.
• Chemical industry. Combined seals with fluoroelastomer and PTFE resist concentrated acids and alkalis at temperatures up to +260 °C. In batch reactors, they withstand frequent changes in the composition of the medium.
• Food production. Elastomers must have permissive documentation for contact with food products, and also possess a smooth surface that prevents the accumulation of bacteria.

At large pumping stations, wafer seals often operate under conditions of frequent water hammer, therefore when selecting, preference is given to reinforced combined constructions described in the combined wafer seal catalogue. In fire‑fighting water mains, maintaining leak‑tightness after prolonged inactivity is critical — here seats with minimal compression set have proven themselves well.

8. Torque Calculation and Actuator Requirements

The choice of seal type affects the torque that the valve actuator must develop. Seals made of soft elastomers require less torque, but at high pressures they may bind. Combined seals with fluoroplastic surfaces and metal springs create a stable torque over the entire pressure range. When selecting an actuator, reference is made to the manufacturer’s catalogue, in which the required torque with a 30 % margin is indicated for each diameter and pressure.

Particularly stringent requirements are imposed on actuators for valves with disc‑type multi‑layer seals. Their closing torque can exceed the torque for rubber seats of the same diameter by one and a half to two times. This is explained by the larger contact area and the need to compress the graphite layers. However, such costs are justified by the service life: disc‑type seals operate without replacement for up to 10–15 years under the most severe conditions.

9. Storage and Transportation

Elastomer parts require careful handling. They are stored in polyethylene bags, protected from direct sun, ozone and heat. The warehouse temperature must lie in the range 0…+35 °C. Storing seals near electric motors or furnaces is not permitted. The shelf life of EPDM is up to 5 years, NBR — up to 4 years, FKM — up to 10 years. The metal parts of combined seals are preserved with anti‑corrosion grease. Before installation, the preservative grease is removed with a solvent that leaves no traces and does not damage the elastomer.

Transportation must exclude mechanical compression of the seals, since prolonged stay in a deformed state leads to compression set. Large‑diameter rings are transported on edge or in special foam plastic cradles.

10. Standards and Certification

The production and testing of wafer seals are regulated by GOST 28759.1‑90, GOST 28759.2‑90, as well as international standards EN 593, API 609, ISO 5752. For seals in contact with drinking water, a certificate of conformity to SanPiN is mandatory. For products intended for hazardous production facilities, a passport is issued indicating the materials, allowable pressures and temperatures, as well as the results of acceptance tests. For deliveries to the countries of the Customs Union, TR CU 010/2011 applies. The certificates must be valid at the time of shipment, and the marking on the packaging must contain the EAC mark.

11. Conclusion

A wafer seal is not a consumable but a technically complex element on which the leak‑tightness and service life of pipeline valves depend. A wide range of types and materials makes it possible to cover the demands of virtually any industry. Proper selection, compliance with installation technology and regular inspection guarantee the stable operation of valves over many years. To view the full product range, please refer to the pages disc‑type wafer seal and combined wafer seal, where detailed technical characteristics and drawings are presented.