ADVANTAGES:
Good shutoff capability
Moderate to good throttling capability
Shorter stroke (compared to a gate valve)
Available in tee, wye, and angle patterns, each offering unique capabilities
Easy to machine or resurface the seats
With disc not attached to the stem, valve can be used as a stop-check valve
DISADVANTAGES:
Higher pressure drop (compared to a gate valve)
Requires greater force or a larger actuator to seat the valve (with pressure under the seat)
Throttling flow under the seat and shutoff flow over the seat
The following are some of the typical applications of Globe valves:
Cooling water systems where flow needs to be regulated
Fuel oil system where flow is regulated and leaktightness is of importance
High-point vents and low-point drains when leaktightness and safety are major considerations
Feedwater, chemical feed, condenser air extraction, and extraction drain systems
Boiler vents and drains, main steam vents and drains, and heater drains
Turbine seals and drains
Turbine lube oil system and others
What is a Needle Valve?
A needle valve is a type of valve which can be used to regulate flow of a substance, usually either gas or water, through an appliance or system. The unique feature of the value is the inclusion of a small plunger, with a shape akin to a needle. The plunger features a small handle, known as a handwheel, to enable easy and precise turning of the valve. When fully attached, the elongated end of the valve fits exactly into what is known as the seat, a part of the appliance that is being regulated. However, if the valve is turned, space opens up between the needle and the seat, which will result in a minimal amount of substance able to pass through the needle valve.
One design feature of most needle valves dictates that a considerable number of turns are required to make even a small amount of space open up. This enables gradual, accurate and precise control over the amount of liquid/gas that can pass through the valve. Additionally, this can prevent damage to gauges which could be affected by sudden bursts of liquid/gas, and allows for better control and regulation in general. Some types of needle valves are connected to an automated system and do not require manual regulation. These will either operate on timers or respond to external data to regulate the closure and opening of the valve as appropriate. These can be found in many types of engines and gas piping. This allows for the operation of the valve to be optimal for the substance and system that it is required for and will likely reduce the chances of damage through incorrect operation of the valve.
Needle valves are commonly made of robust and durable materials, such as copper or steel. However, valves made from plastic and brass are sometimes used depending on the specific requirements of the valve.
How are needle valves used?
Needle valves are used in many different systems and applications, often featuring in carburettors. Needle Valves can also be found in some water heaters, used to regulate pressure inside a device. This can also ensure that the appliance is running at maximum efficiency, without excess water being used. In larger scale usage and delivery to numerous consumers, needle valves can be used to regulate delivery of a product and relieve pressure on the systems used to distribute the relevant substances. Needle valves are also sometimes used in vacuum systems, in order to release a controlled yet steady supply of gas without a great amount of pressure. The valve allows supply of gas to be slowed down considerably before being shut off. This can minimise stress and strain on internal machinery and components.
One hindrance of using needle valves is the lack of visual feedback regarding exact amounts of pressure being placed upon a system. As the entire operation of the valve takes place inside machinery/piping, it is impossible to gauge this from sight. There are instances of additional devices being installed allowing operators to monitor levels of pressure being exerted upon a system. With automated needle valve systems, this is less of an issue. Needle valves, by their design, allow pressure to be added/relieved in very small increments. Needle valves are invaluable for many systems and machines, as they help to maintain these and prevent significant damage.
