Triple-Offset and Resilient Seated Butterfly Valves

In 1992, Curtiss-Wright Nuclear introduced the first Safety-Related and ASME Code triple offset butterfly valves to the nuclear power industry through its PermaSeat product line. Today the triple offset valve design has been installed in almost every U.S. plant and plays a critical role in the safe and efficient operation of a nuclear reactor.

With over 25 years of nuclear operating experience, PermaSeat butterfly valves have proven to be effective and reliable in both modulating and isolation applications.

Beyond the triple-offset butterfly design, PermaSeat also provides large diameter butterfly valves (80" and higher), as well as both high performance and rubber-lined designs. This extensive portfolio of butterfly valves is one of the largest in the industry that can improve the reliability of plant systems, solve industry obsolescence issues, and support subsequent license renewal.

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Models

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Triple Offset

The PermaSeat TOSV butterfly valve is a dedicated triple offset geometry design. This particular feature eliminates the disc-to-seat rubbing condition, normally associated with high performance butterfly valves, which induces wear of varying degrees, even in metal seated versions.

Key Features and Benefits

Triple Offset Design	Eliminates unnecessary wear and prolongs seat and seal life
Ease of Maintenance	Field replaceable seat and seal ring
Bi-Directional Shut-Off	Provides zero leakage capability
Non-Galling Design	Enables a wide variety of material options
Additional Features	Live loaded packing, double block and bleed design, gate valve replacement design

Principles of Operation

The offsetting of the shaft in two axis, when combined with the tilting cone / ellipsoidal segment means that there is complete removal of 'scuffing' and surface pick up during the full 90 degree movement. The seal ring, which is of laminated construction, uses the seat ring as the stopping point, eliminating separate mechanical stops. There is no need for critical settings for disc-to-seat contact to achieve required shut-off. This is beneficial in situations where actuators and controls are fitted.

When closed, the seat is bi-directionally tight, with a zero leakage rate in either direction. The seat sealing load is torque induced, thus when the disc movement reverses to 'open', the operating torque quickly reduces, due to the on / off contact action of seal to seat and swing clear action via shaft offsets. Since the seal action is 'contact' without 'rubbing' action, then galling does not occur, allowing the same material to be used for both seal and seat.

General Specifications

Size:	3" to 84"
Ratings:	ANSI Pressure Class 150 to 2500
Connections:	Wafer Flangeless, Wafer Lugged, Double Flanged (short and long patterns), and Butt Weld
Quality Class:	Commercial, Safety-Related ASME Section III

Plant Design

PWR, BWR, CANDU

Typical Plant Applications

Service Water
Component Cooling Water
Containment Purge/Vent Isolation
Alt. Decay Heat Removal, RHR System
Radiation Waste Control Isolation
Air Header System
Sump Floor Drain-Containment Isolation
Heater Drain
Condensate Polishing
Condensate/Feedwater Loop
Hydrogen Cooler Heat Exchanger System
Raw Water Treatment

Available PermaSeat Products

TOSV Series – Triple Offset Butterfly Valves
R&E Series – Large Diameter Butterfly Valves
T Series – High Performance Butterfly Valves
C Series – Rubber Lined Butterfly Valves

Resilient Seated

PermaSeat Resilient Sealed Valves are suitable for isolation and flow control applications and have a proven record for reliability over the past 30 years for applications in seawater cooling, circulating water systems, and condensate systems.

The ease and flexibility of material selection enables both simple and arduous applications alike to be within the capability of this valve series.

Key Features and Benefits

Single or Double Offset Design	Excellent for both isolation and control duties
Ease of Maintenance	Integral body seat, individual seat, or resilient seal ring are field replaceable
Positive Shut-Off	Achieved without excessive interference between seat and seal ensuring maximum seal life and low seating and unseating torques
Ebonite Liner	Enables a wide variety of material options
Additional Features	Effective in high-chlorine environments such as brackish water and seawater, where the natural resistance of Ebonite insulates the wetted portions of the valve body from corrosive attack by such aggressive media

Principles of Operation

The valve is a bi-directional tight shut-off device incorporating a resilient seal mechanically retained around the periphery of the valve disc. The seal is available in various types of elastomers, the selection being dependent on the valve duty and working pressure and temperature. The seal seats against a metal face machined into the body of the valve. Positive shut-off is achieved without excessive interference between seat and seal ensuring maximum seal life and low seating and unseating torques.

The E-Series has an ebonite lining which is a hard, natural rubber, bonded and autoclave cured to achieve maximum strength and adhesion. It has a corner locking overlap feature around the flange and shaft bores to maintain optimum stability. The seat contact area, against which the resilient disc seal ring locates, is fully machined to ensure consistently tight shut-off.

In operation, there is a key difference when compared with other rubber lined valves. The ebonite is part of the structural rigidity of the body and the resilient seal is disc located. This is the element being compressed during sealing on closure. This eliminates dragging on the liner, which occurs on other valve designs where the disc is solid and the seal is made by compression of the liner. It is particularly effective in high-chlorine environments such as brackish water and seawater, where the natural resistance of Ebonite insulates the wetted portions of the valve body from corrosive attack by such aggressive media. The use of Ebonite in this application allows the use of Carbon Steel valve bodies, and actually makes them more corrosion-resistant than stainless-steel bodies in brackish water applications.

General Specifications

Size:	2" to 144"
Ratings:	ANSI Pressure Class 150 to 300
Connections:	Double flanged, wafer lugged and wafer flanged
Quality Class:	Commercial, Safety-Related, ASME Section III