What is a rising stem globe valve?
The rising stem globe valve is a linear motion valve mainly designed to stop, start and regulate flow. The disc of the rising stem globe valve can be completely removed from the flow path, or the flow path can be completely closed. The rising stem globe valve regulates the flow in the pipeline and provides positive shut-off capabilities. The rising stem globe valve has a cast steel valve body, valve trim and flange connection. The valve is operated by a rising rod.
rising stem globe valve is a type of gate valve which is able to follow the opening/closing position by moving the stem up & down movement, is able to follow electronically the movement by adding a monitoring key, and full open position does not disrupt the flow. rising stem globe valve generates low head loss according to butterfly valves.
Since the entire system pressure exerted on the disc is transmitted to the valve stem, the actual size of these valves is limited to NPS 12 (DN 300). The rising stem globe valve larger than NPS 12 (DN 300) is an exception rather than a rule. Larger valves require tremendous force on the valve stem to open or close the valve under pressure. The rising stem globe valve up to NPS 48 (DN 1200) has been manufactured and used.
The rising stem globe valve is widely used to control flow. The flow control range, pressure drop and load must be considered when designing the valve to avoid premature failure and ensure satisfactory service. Valves that withstand high differential pressure throttling services require specially designed valve trims. When minimum restrictions are required, the gate valve design makes it ideal for the free flow of fluids. When the gate valve is fully opened, the gate is completely sucked into the valve body, so that the pressure and flow through the valve are consistent with the connected pipeline.
Generally, the maximum pressure difference on the valve disc should not exceed 20% of the maximum upstream pressure or 200 psi (1380 kPa), whichever is less. The rising stem globe valve with special internals can be designed for applications that exceed these differential pressure limits.
Rising stem globe valve Accessories
Rising stem globe valve accessories usually include disc and valve seat and rising stem globe valve stem
Disc: The most common disc designs of rising stem globe valve are: ball disc, combination disc and plug disc. The ball and disc design is mainly used in low pressure and low temperature systems. It can throttle, but in principle it is used to stop and start the flow.
The combination disc design uses a hard non-metallic insert ring on the disc to ensure a tighter closure.
The plug design provides better throttling than the ball or combination design. They have many different designs, and they are all long and tapered.
Valve seat: The rising stem globe valve seat is integrated or screwed into the valve body. Many rising stem globe valves have back seats in the valve cover. The back seat provides a seal between the valve stem and the valve cover and prevents system pressure from affecting the valve filling when the valve is fully opened. The back seat is often used for rising stem globe valve.
Stem: rising stem globe valve uses two methods to connect the disc and the stem: T-slot and disc nut structure. In the T-slot design, the disc slides on the stem, while in the disc nut design, the disc is screwed into the stem.
Structure of Rising Stem Globe Valve
The rising stem globe valve usually has a rising stem, and the larger size is an external thread and yoke structure. The components of the rising stem globe valve are similar to those of the gate valve. This type of valve has a valve seat on a plane parallel or inclined to the flow line.
The rising stem globe valve is relatively easy to maintain, because the disc and valve seat are easy to refurbish or replace. This makes the rising stem globe valve particularly suitable for services that require frequent valve maintenance. In the case of manual operation of the valve, a shorter disc stroke has advantages in saving operating time, especially when the valve is frequently adjusted.
The main change in the design of the rising stem globe valve is the type of valve disc used. The plug-type disc has a longer tapered structure and a wider bearing surface. This type of valve seat can resist the erosion of fluid flow to the greatest extent. In the composite disc, the disc has a flat surface that presses on the seat opening like a cover. This type of valve seat arrangement is not suitable for high pressure differential throttling.
In cast iron rising stem globe valves, the disc and seat ring are usually made of bronze. In steel rising stem globe valves with temperatures up to 750°F (399°C), the valve trim is usually made of stainless steel, so it has the ability to resist seizure and wear. The mating surfaces are usually heat treated to obtain different hardness values. Other decorative materials are also used, including cobalt-based alloys.
The surface of the valve seat is ground to ensure that the full bearing surface is in contact when the valve is closed. For lower pressure levels, the alignment is maintained by a long disc lock nut. For higher pressures, the clapper guide is cast into the valve body. The valve flap rotates freely on the valve stem to prevent the surface of the valve flap and the seat ring from wearing. The valve stem rests on the hardened thrust plate, eliminating the abrasion of the valve stem and the disc at the contact point.
Flow of rising stem globe valve
For low temperature applications, the rising stem globe valve is usually installed below the valve clack. This helps simplify operations and helps protect the packing.
For high temperature steam applications, install the rising stem globe valve to make the pressure higher than the disc. Otherwise, the valve stem will shrink as it cools and tend to lift the valve clack from the valve seat.
The Advantages & Disadvantages of Rising Stem Globe Valve
Advantages:
Good shut-off capability
Moderate to good throttling ability
Shorter stroke (compared to gate valve)
Provide T-shaped, Y-shaped and angular patterns, each pattern has a unique function
Easy to process or rework the seat surface
The disc is not connected to the stem, the valve can be used as a stop check valve
Easy to open and close.
Small fluid resistance, sealing surface by medium erosion and erosion.
Medium flow is not restricted, no turbulence, no pressure reduction.
The sealing surface is easy to be eroded and scraped, difficult for maintenance.
Larger structure requires more space and long-time opening.
Disadvantages:
Higher pressure drop (compared to gate valve)
Need more force or larger actuator to fix the valve (there is pressure under the valve seat)
Throttle flow under the valve seat and shut-off flow on the valve seat
Typical application of rising stem globe valve
Applications of rising stem globe valve
The following are some typical applications of rising stem globe valve:
The cooling water system that needs to adjust the flow
Fuel system that regulates flow and seals are important
When tightness and safety are the main considerations, high-point vents and low-point drains
Water supply, chemical feed, condenser extraction and extraction drainage systems
Boiler vents and drains, main steam vents and drains, and heater drains
Turbine seals and drain pipe
Turbine lubricating oil system and others
What's the difference between rising stem globe valve and non-rising stem globe valve?
◆ The rising stem globe valve can be seen from the appearance whether the valve is closed or open. The lead screw can be seen while the non-rising stem globe valve cannot.
◆ The ascension screw of rising stem flanged gate valve is exposed outside, the nut cling to the handwheel is fixed (not rotating axial movement), the rotation of the screw and gate only relative motion without relative axial displacement of the disc and stem up and down together. The lifting screw of the non-rising stem flange gate valve only rotates and does not move up and down.
