Bleed, relieve, purge—these terms are often used interchangeably, but when it comes to their labels as industrial components, they aren’t exactly the same thing. If you need a new valve for your hydraulic system, you may be unsure whether a bleed valve, relief valve, or purge valve is the right component for the job.
Below, we’ll discuss how these valves differ and how to use them in hydraulic settings. Keep reading to learn where to find quality valves and fittings from Hy-Lok Canada!
What Is a Bleed Valve?
A bleed valve is a component used to isolate or block fluid flow in hydraulic and pneumatic systems, allowing fluid to be removed from a tank or tube while regulating pressure.
This type of valve uses a threaded bleed screw to open and close, and can be easily integrated into a fluid control system with male and female NPT, ISO, and SAE thread connections.
What Is a Purge Valve?
Purge valves serve a similar function to bleed valves, but their venting mechanism differs slightly. Purge valves use a poppet-and-spring system rather than a threaded screw to open and close. They also contain a vent hole to drain excess fluid and prevent pressure build-up.
What Is a Relief Valve?
A relief valve is used to control or limit pressure in a system so that pressurized fluid can flow out of the system through the passageway. This prevents equipment failure, ensuring the system isn’t under too much pressure during operation.
Unlike bleed and purge valves, relief valves are not manually operated. Once you set the required pressure range, these valves automatically regulate the pressure for liquid and gas flow.
How These Similar Industrial Components Differ
While these three components perform very similar functions, they cannot necessarily be used interchangeably. Their release styles and operation are their key differentiators, which impact how they can be used in industrial applications.
Let’s break these differences down:
Release Style
Bleed valve: These valves are manually operated and built with a threaded bleed screw to release and close. In addition to bleeding liquids and gases, they also allow you to control the direction of the outflow with a vent tube.
Purge valve: These valves are also manually operated and feature a poppet and spring system to release and close. Unlike bleed valves, purge valves do not direct the outflow of liquids and gases in a specific direction.
Relief valve: These valves automatically direct liquid flow paths. Unlike bleed and purge valves, they also have the ability to direct fluids back into the system via a threaded or compression output.
Operation
Bleed valve: Used in high-pressure, extreme-temperature environments, our bleed valves from Hy-Lok operate at pressures up to 10,000 psig and temperatures from -65°F to 850°F.
Purge valve: Intended for medium- to high-pressure, high-temperature environments. Hy-Lok’s purge valves operate at pressures up to 4,000 psig and temperatures from -65°F to 600°F.
Relief valve: These auto-controlled valves are intended for low- and high-pressure environments and medium temperatures.
Our relief valves from Hy-Lok operate up to 3,000 psig for low-pressure applications, and up to 6,000 psig for high-pressure applications. They also accommodate temperatures from -10°F to 400°F.
When to Use a Bleed, Relief, or Purge Valve
So, when should you use a bleed, relief, or purge valve?
Bleed valves are ideal for venting media before beginning maintenance, calibration, or media analysis on a line containing high-pressure materials.
Purge valves can be used for the same purpose, but are intended for systems that use a poppet and spring rather than threads. They also cannot be used in an application that requires directional control for the vented liquids.
Finally, relief valves can be used for both venting and redirecting the flow of liquids and gases from a system. The excellent pressure relief mechanisms make these valves ideal for protecting pumps, storage tanks, and pressure vessels from explosions.
Get Quality Valves, Fittings, and More from Hy-Lok Canada
Whether you need a purge, relief, or bleed valve for your industrial application, you can find what you need from Hy-Lok Canada! Contact us today to place an order and maintain precise flow control in your hydraulic equipment.
Do you require a regular supply of valves and fittings for your worksite? Ask about our local vendor management services!