Key Takeaways
- Globe valves are the conventional choice for steam throttling because the plug and seat geometry gives fine, repeatable control across the travel range.
- The trade-off is pressure drop. The flow path through a globe valve turns twice, which costs head. In steam throttling that loss is usually acceptable because control is the priority.
- Globe valves do not give quick shutoff. They are multi-turn valves, so they are a poor choice where fast isolation is required.
- In clean saturated steam, a globe valve is a sound selection. In steam carrying condensate, scale or flashing solids, seat erosion becomes the limiting factor and the valve life drops sharply.
- Where steam service includes solids, such as boiler blowdown, a metal-seated self-lapping design outlasts a conventional globe valve because the sealing surface is renewed rather than eroded.
Losses from downtime total $864 billion a year for Fortune Global 500 industrial companies. You can’t afford unplanned system failures. No matter how steam fits into your production, you need the system to perform reliably. High-quality valves are critical to keep your operations running smoothly.
Many businesses choose a globe valve for a steam application. Learn more about glove valves and the other options for your steam system.
Using a Globe Valve for a Steam Application
Globe valves are multi-turn linear valves. Globe valves have a moveable plug or disc between two halves of the valve body. The disc controls the flow between the two chambers. Raising the plug allows media to flow from one half of the valve body to the other. Lowering the plug stops the flow. Multiple turns are necessary to fully open and close the valve.
Globe valves can create large drops in pressure. They’re a common choice for steam applications, though. The flow needs throttling, but the amount of pressure loss isn’t a primary concern.
Shutoff and Throttling
Globe valves can provide shutoff and throttling. Globe valves won’t provide a quick shutoff like a ball valve or butterfly valve, though. Globe valves create moderate to strong throttling. A globe valve is a better choice for flow regulation than other multi-turn linear valves like gate valves. Globe valves provide finer control than quarter-turn valves like ball valves.
Easy to Maintain
The design of a globe valve makes it easy to maintain. The structure is simple. You can replace the disc and resurface the seat if necessary.
Types of Globe Valves
Globe valves come in three main shapes: T or Z, Y, and angle. The different shapes change the flow path. This can reduce the amount of pressure loss.
T or Z Globe Valve
The standard shape for globe valves is the T or Z pattern. T- or Z-pattern valves have the lowest flow rate and a higher pressure drop. They provide the highest throttling capacity.
Y Globe Valve
A Y-pattern globe valve has a more direct flow path than a T-pattern valve. The bonnet and stem meet the valve body at an angle.
Y-pattern valves have less pressure loss. They also have the least flow resistance.
Angle Globe Valve
An angle globe valve has a 90º angle between the inlet and outlet ports. The flow only changes direction once. This reduces pressure loss.
An angle valve can function as a pipe elbow in addition to a valve.
Body-Bonnet Connection
The connection between the valve body and the bonnet is critical for the performance of a steam globe valve. The best type of connection for an application depends on the pressure and temperature requirements.
Screwed Bonnet
A screwed bonnet is a basic design. Screws connect the bonnet and the body. It’s an economical option.
Screwed bonnet globe valves are suitable for applications with medium-pressure requirements.
Bolted Bonnet
Bolted bonnets are the most common design. They use nuts and bolts to connect the bonnet to the body. A gasket provides the seal.
Bolted bonnet globe valves are suitable for high temperatures and high pressure requirements.
Pressure-Seal Bonnet
A pressure-seal bonnet is an option for high-pressure, high-temperature applications. System pressure provides enough force to seal the body to the bonnet. The seal gets tighter as the media pressure increases.
Welded Bonnet
Welded bonnets are economical and reliable. However, you can’t clean or repair them without removing the weld. They’re an option for applications where the valve won’t need maintenance or cleaning.
Materials for Steam Globe Valves
The materials for the housing and seal of a globe valve for a steam application must be compatible with the media. Metal is usually used for the valve body and internal parts like the disc. Metallic materials that can handle steam include:
- Alloy steel
- Brass
- Bronze
- Cast iron
- Copper
- Stainless steel
Rubber-based or plastic-based materials are necessary for components like the gasket and seal. These materials include:
- EPDM
- NBR
- FKM
- PTFE
- PA
They will withstand the heat and pressure of steam applications.
Manual vs Automated Steam Globe Valves
Globe valves can have manual or automated actuation. Manual globe valves have a hand-operated wheel or crank that opens and closes them. An automated system can use electric, pneumatic, or hydraulic actuation.
Electric Valve Actuator
Electric actuators rely on an electric motor and electrical wiring. They provide precise control and flow regulation. The component costs are relatively high, but the operating costs are low.
Pneumatic Valve Actuator
Pneumatic actuators use compressed air. They have a fast cycle time, and they resist moisture and overheating. The installation costs of a pneumatic actuator are lower than for an electric one. The operating and maintenance costs are higher, though.
Hydraulic Valve Actuator
Hydraulic actuators use liquid pressure. They can deliver high force and are very durable. They have limited motion control capabilities, though.
Everlasting Valves for Steam Applications
Globe valves are a common choice for steam applications. However, Everlasting Valves have several advantages over traditional globe valves.
Boiler blowdown valves from Everlasting Valve Company are specially designed for the severe service requirements of industrial steam applications. They use proprietary self-lapping, rotating-disc technology. The rotating disc clears out damaging boiler scale and other particles. This is a significant benefit compared to globe valves. As a globe valve operates, it forces dirt into the valve seat. This reduces sealing and will lead to valve failure. Everlasting boiler blowdown valves need less maintenance and last longer than conventional valves. You can choose from a straight-through flow, angle, or Y pattern. Quick-opening and slow-opening valves are available.
Boiler blowdown valves are ideal for applications such as:
- Steam boiler blowdown
- Surface blowdown
- Water column drain
- Shut-off valve
- Stop valve
Boiler blowdown valves reduce your maintenance costs and minimize downtime. Investing in Everlasting Valves brings a significant benefit to your operations.
Valves for Steam Applications
A globe valve for a steam application is the traditional choice. Everlasting Valve Company has a better solution. Our boiler blowdown valves are a durable and long-lasting solution. They’re ideal for the sludge, high temperatures, and pressure that boilers produce. Everlasting Valves are low-maintenance. They perform consistently even in severe service applications.
Everlasting Valve Company is ISO 9001 certified. Our valves meet ASME/ANSI requirements. Contact us today to find out how we can improve your operations.
Frequently Asked Questions
Yes for throttling clean steam. The linear plug and seat design gives fine control and the valve handles the temperature well with the right body and trim material. They are not suited to fast isolation because they are multi-turn, and they perform poorly where the steam carries solids.
A globe valve is built for throttling and gives good control at partial travel. A gate valve is built for full-open isolation and is damaged by throttling, because flow across a partially raised gate erodes the seat faces. Use the globe valve for control and the gate valve for on-off.
Most commonly from seat erosion caused by wire drawing, where steam passing through a small closing gap cuts a channel into the seat face. Thermal cycling and condensate carrying scale accelerate it. Once wire drawing starts, the valve will not reseal without trim repair.
Blowdown water carries sludge, scale and silica, and it flashes across the valve. Solids reach the seat during every cycle and the flashing erodes the trim. Globe valves have no mechanism for clearing solids out of the sealing area, so the seat degrades cycle by cycle.
A metal-seated valve that clears its own sealing surface. Everlasting’s rotating disc wipes the precision-lapped seat on every operation, so solids are pushed away from the sealing path and the surface is re-lapped rather than eroded. That is why the design is used in boiler blowdown, where globe valves are routinely replaced.