Double Expanding
Gate Valves
How Does It Work
The Expanding Gate Valve achieves its
sealability by mechanically expanding
the 2-piece obturator assembly (gate
and segment) against the seats.
The gate is attached and driven
by the stem and a centralizer
mechanism retain the gate segment
assembly during the open and closing
travel. The valve must be torqued fully
open or fully closed to seal properly.
This design prevents damage
to the sealing surfaces of the gate
and seat and isolates the body
cavity preventing buildup of foreign
material, increasing the life
of the valve.
Fully Closed
In the full expanded closed position,
the segment has engaged the lower
stop and the gate is wedged downward,
expanding the gate and segment
against the upstream and downstream
seats forming a tight mechanical seal.
Mid Position
During open and closing travel,
the gate-segment assembly the gate
travels across the wedge angle of the
segment. The centralizer mechanism
allows the gate and segment assembly
to travel freely without sticking or
wedging preventing relative movement
between the gate and segment.
Fully Open
In the full expanded open position,
the segment has engaged the upper
stop and the gate is wedged upward
expanding the segment and the gate
into the seats sealing against both
seats. This protects the seat faces
from line flow, while isolating the body
cavity from the flow bore.
Seat and Disc
The 2-piece obturator and the seats
are manufactured from forged steel.
Both are HVOF Tungsten or Chrome
carbide coated. Sealant can be
injected, as a temporary solution
when damage occurs in the sealing
members.
Stem Design
and Seal System
The valve is engineered with rising
stem. The standard stem seal is with
braided graphite and can be fitted with
an emergency grease injection device.
In the event of a gasket failure, this
feature allows restoring of the sealing.
Double Block
and Bleed
The DBB design is a standard feature
of the Viar Valvole double expanding
gate valve . When the valve is in fully
closed position, pressure and or fluid
in body-bonnet cavity can be released
through the body drain system.
In the same position, a double
isolation between the two sides
of the valve is achieved.
Relieving Device
Expanding Gate Valve design will
trap pressure in the valve body cavity
when the valve is in the full open or
closed position. To protect the valve
from overpressure, in case of fluid
thermal expansion and, generally,
when pressure in the body cavity
exceeds the pipeline pressure,
the valve can be provided with upstream
relief piping/valve which relieves
excess body pressure in excess
to the upstream side.
Full Bore Through
Conduit
The pressure drop is minimized without
any turbulence. The valve is Piggable:
Pigs and scrapers can be run through
the valve without damages to the valve.
Optional Features
• Material Options (CRA Alloys
for Very Corrosive Service Media)
• Seat & Stem Sealant Injection System
• Actuation
Benefits
• Gas Tight, Metal to Metal Sealing
• Corrosion Resistant
• Easy Maintenance
• High Pressure / High Temperature
• Bi-directional Sealing
• Fast Closing
• Fire Safe.
