Today Professor Jim talk about Gate Valves
:hello and welcome to a very special episode of IV university where you can get you PVF degree for free. Today we are going to talk about a very special item of the PVF world, the gate valve. In fact this class is so special we are going to lead off with a “Did you know”
Did you know¬¬__ did you know, these gate valves are named after Sluice(sloos) gates.___The dutch controlled water in the canals in the 1200’s, with sluice gates. In the 1300 the Italians made these gates were you could raise or lower them. Which helped them in using the gates for waste water and mining operations.
: The modern gate valve works quite simply: Like the sluice(sloos) gate, the wedge in modern gate valves moves up and into the body of the valve above the port openings.
: when the Wedge goes UP it of course is open Open….And when the valve is closed the disc is literally wedged between two seating surfaces.
: the wedge gate valve which is the most common gate valve design, has over 20 componants to it
: as you can see from this document here, it can be quite daunting trying to learn all the parts of this common valve.
: so to simplify it for you… we will go over the 6 main parts to the valve with this cut out.
: The Body, Bonnet, Gate, packing, gasket, stem and Handwheel. The valve is opened when the gate is raised so that it no longer obstructs flow in the port opening. The gate is raised by the turning of the handwheel counter clockwise and closed in the opposite direction.
: The gate valve has 2 main stem types. Non rising and rising stem
: rising stem . the handwheel stays stationary and the stem extends out of the handwheel which is also an indicator that the valve is open or closed. When open the stem rises. This will let you know in hard to reach or get to areas if the valve is indeed open. Most rising stems have the threads exposed with the threaded bushing at the top of a yoke. These are known as outside screw and yoke (OS&Y) valves
: The non rising stem or commonly written as an NRS stem
: , would be used for areas in which there might not be the clearance to open and close the valve. it has internal threads that the disc moves up and down to open and close the valve.
: Now let’s talk about pressure.
: The Body, Bonnet, gasket, stem and packing form the pressure boundary. These components keep the pressure inside the valve which is very important. Since the stem movement is essential to the operation of the valve.
: The connection and design of how the Body and Bonnet assembled and secures can vary. Most valves above 2” have a bolted body bonnet connection with a gasket sandwiched between them.
: Other connections exist such as union, welded, threaded and pressure seal bonnets exist. Make sure to check your specs for which one is needed when quoting.
: OK so now that you know what the gate valve is, lets talk about the advantage and disadvantages of the valve are.
Advantages of using Gate Valves:
• Economical design (generally the lowest cost valve design)
• Good positive shutoff and sealing.
• Simple design makes it easy to manufacture, maintain and repair
• Most Gate Valves are bidirectional and therefore they can be used in either direction.
• Low pressure drop across the valve.
The major drawbacks to the use of a Gate Valve are:
• The multi turn design requires more time to open or close.
• Gate Valves are not suitable to regulate or throttle flow. Severe vibrations can occur and can destroy the valve.
• They are sensitive to vibration.
: OK class we are coming to the end, so lets do a quick review
: So to review The modern gate valve works by the wedge in gate valves moves up and into the body of the valve above the port openings. when the Wedge goes UP it is open Open….And when wedged between two seating surfaces it is closed.Off camera: the Bonnet is device that provides leak proof closure for the valve body. It contains “packing” a wearable material that ,contains the seal between the bonnet and stem during valve cycling operations: These valves have 2 main types of stems the rising and the non rising is used when area is restricted.
