Precision is the watchword when it comes to needle valves.
WHAT ARE NEEDLE VALVES?
Much like the globe valves we talked about last week, needle valves are control valves. They share some of the same design features and have similar benefits.
Both allow the operator to change flow rate and use a threaded rotating stem to adjust that rate. The difference is precision.
Needle valves are valued for their use in calibration because they can be so finely tuned.
The valves can also provide positive shutoff, so that gauges and other measurement instruments may be installed or removed safely.
The valves are used in a wide variety of industries, including petrochemicals and biofuels.
WHY ARE THEY CALLED NEEDLE VALVES?
A needle valve gets its name from its business end: a conical, needle-like plunger that fits exactly into a valve seat. As the stem rotates, the needle is raised or lowered into the seat, increasing or decreasing flow as it moves. The change in needle position is minimal with each turn, allowing fine tuning of flow.
The fine threading of the valve stem gives it great mechanical advantage, meaning it can be sealed with minimal force from the operator.
WHAT'S THE DOWNSIDE TO NEEDLE VALVES?
The downside of that ease of operation, however, is that its open or closed nature cannot be determined by visual inspection alone.
HOW DO THEY WORK?
The seat is designed to fit the needle exactly, providing a seal that can operate at high pressure ratings.
The DuraChoice needle valves we sell are rated at 10,000 psi at normal operation temperatures.
Part of the reason needle valves can take so much pressure is their size. The valve’s opening, or “orifice”, is generally small, compared to the rest of the valve’s body. While this makes the valve great for high pressure projects, it means the valve’s flow rate is relatively low.
However, this is not usually a problem when you consider how the valves are used. They work well for processes which require precise control of gas flow. We sell a lot of needle valves along with vacuum gauges, for use in projects like gas lasers or to regulate the filling of voltage regulator tubes.
HOW ARE THEY USED?
Needle valves are common in engines with carburetors because of they can be used to finely dial in fuel. That precision is important, because too much fuel will begin to flood the engine causing the fuel/air mixture to suffer and killing the motor.
If there is not enough fuel flowing into the carburetor, the engine is forced to work harder, making it less effective and possibly causing damage over time.
Needle valves can be found in utility equipment used to measure water or natural gas consumption. Because the rate of delivery is kept constant by the valve, there is little unintended variation.
The valves are also used at distribution points as well, to regulate the flow delivered into the system. Operators at the production level are able to determine how much gas, water, etc., to put into the system, lowering or raising it as the need arises.
They may also be used as “bleed” valves in residential water heater systems to relieve pressure on the water flowing through the heater.