Through conduit slab gate valves are usually used for the oil & gas pipe-lines. 
Through conduit slab gate valve are manufactured with a full bore, slab gate, rising stem OS&Y and floating seats. Slab gate is a simple solid gate design, featuring metal-to-metal seal between gate and seats, to apply for the most severe service condition, including corrosive and abrasive fluid environments. A floating seat is designed to match the slab gate. A belleville spring and O-ring between each seat and body ensure a tight seal against the slab gate. The floating slab gate uses the natural force of line pressure to obtain a dynamically tight downstream seal in high-pressure differential applications. Low-pressure sealing is accomplished with an o-ring that energizes the seat and minimizes corrosion and debris build up. Common trims are available.

Double block and bleed capability and automatic relief of excess body pressure are standard feature of this seat design.

The smooth, continuous bore minimizes turbulence within the valve and when in the open position it produces a pressure drop equivalent to a portion of pipe of same length and diameter. The seat faces are outside the flow stream and therefore protected from the erosive action of the flow. Pigs and scrapers can be run through the valve without damage.
Through Conduit Slab Gate valve design minimizes and eases the maintenance allowing for the service operations to be done without the removal of the valve from the line.

Features of Through Conduit Slab Gate Valves:

Full bore through-conduit port, Fully piggable
Floating slab gate
Spring/pressure loaded seat ring with relief valve 
Bubble tight shut off at high and low pressure 
Bi-directional operations 
Double Block and Bleed performance available 
Seat faces protected from erosion by flow 
Position indicator 
Top entry assembly for on-line maintenance 
Various actuation (Electric, Pneumatic and Hydraulic actuators)

Applicable standards of Through Conduit Slab Gate Valves:
a) Design & Manufacture: API 600, API 6D, BS 1414
b) Face to Face: API 6D, ASME B16.10, EN 558
c) Connection End: ASME B16.5, ASME B16.25, EN 1092, EN 12627, JIS B2220
d) Test : API 598, API 6D, EN 12266

Sizes: 2" - 48" or DN50 - DN1200
Pressure Rating: Class 150 - Class 2500 or PN 16 - PN 420        
Valve Materials: WCB, LCB, WC6, WC9, C12, C5, CF8, CF8M, Duplex Stainless Steels, etc. 
Operated by: Handwheel, Gear, Pneumatic, Hydraulic and Electric actuator