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Valve Seating Mechanisms Explained

1. Single piston effect seats are self-relieving, allowing trapped media pressure in the valve body cavity to overcome the seat spring force and push the seat ring away from the ball. 2. Double piston effect seats are not self-relieving. Trapped media pressure in the valve body cavity acts to push the seat ring against the ball regardless of pressure source. 3. A valve with two single piston effect seats has a double block and bleed (DBB) design, while a valve with two double piston effect seats has a double isolation and bleed (DIB) design.

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486 views1 page

Valve Seating Mechanisms Explained

1. Single piston effect seats are self-relieving, allowing trapped media pressure in the valve body cavity to overcome the seat spring force and push the seat ring away from the ball. 2. Double piston effect seats are not self-relieving. Trapped media pressure in the valve body cavity acts to push the seat ring against the ball regardless of pressure source. 3. A valve with two single piston effect seats has a double block and bleed (DBB) design, while a valve with two double piston effect seats has a double isolation and bleed (DIB) design.

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prihartono_dias
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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DBB vs.

DIB
Call: 1.866.722.7722
Email: order@meridianvalve.ca

VALVE BODY GASKET O-RING SEAT RING VALVE CAVITY

How Do Single Piston Effect Seats Work? SEAT INSERT

SPRING

1. During normal operation, upstream or downstream pressure BALL

in combination with force created by the seat springs


pushes the seat ring against the ball creating positive

A1

A2
shutoff (A1>A2).

2. With media trapped in the body cavity any increase in media


pressure attempts to push the seat ring away from the ball
(A3). As pressure in the cavity continues to increase a
A4

A3

point is reached where the pressure in the cavity can now


overcome the spring force and any other forces (A4).

The resultant force pushes the seat assembly away from the
ball (A3>A4). Seat assemblies with this feature are referred
Pressure acting in the body cavity allows to as self relieving.
self relieving of the seat
A valve with two single piston effect seats has a double block
and bleed (DBB) design.

How Do Double Piston Effect Seats Work?

1. During normal operation, upstream or downstream pressure in


combination with force created by the seat springs pushes the
seat ring against the ball creating positive shutoff (A1>A2).

2. With media trapped in the body cavity any increase in


media pressure acts to push the seat ring against the ball
(A3). As a result, regardless of whether the pressure is
from upstream, downstream or within the body cavity, the
seat ring is always pushed against the ball.

The movement of the seat ring against the ball is created


due to differences in the effective pressure influenced area
of the upstream and downstream side of the seat assembly
(A3>A4). Seat assemblies with this feature are not self
Resultant pressure acting in the body cavity
pushes seat against the ball.
relieving.

A valve with two double piston effect seats has a double


isolation and bleed (DIB-1) design.
R2001 PLU 11 2015

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