Low pressure/high volume (LP/HV) valves are versatile systems which provide proper flow control in a wide range of medical, industrial, and commercial applications. Valves control the flow of large volumes of gasses or fluids at low working pressures – typically 36 lb per square inch gage (psig) or less. Applications that frequently use LP/HV valves include fluid or gas sampling systems, oxygen concentrators, air beds and other applications for systems that need to control a large volume of media at low pressure. (See sidebar, below)
How they work
Typically, LP/HV valves consist of two ports (input and output) connected via a common orifice through the valve body. They are similar to conventional valves but with much larger orifices to permit higher flow rates. Most high-volume valves use poppet-style valve mechanisms to compensate for the large openings (Figure 1). LP/ HV valves are available in both normally closed (NC) and normally open (NO) configurations, but NC is more common. The NC-style valve shown in Figure 1 uses a solenoid-operated stem with a poppet to cover the internal passage. A spring holds the poppet in the closed position until the solenoid is energized. When energized, the stem with poppet pulls away from the seat, allowing air to flow through the valve. Actuation voltages for these valves can vary, but most products can be specified for 12VDC or 24VDC. Since the spring is the only mechanism keeping the valve closed, the working pressure of the system it’s controlling must not exceed the force it can exert on the poppet. This limit is referred to as the valve’s rated working pressure.
LP/HV valves can be configured to support mono-directional or bi-directional flows (Figure 2). In bi-directional valves, the retention spring is enhanced to counteract the additional forces created during reverse-flow operation. As with mono-directional valves, care must be taken to not exceed the bi-directional valve’s rated working pressure.
Since LP/HV valves offer significantly less restriction than conventional valves, it takes less energy to pump an equivalent volume of fluid through them – lower actuation pressure demands less power to operate. LP/HV valves’ poppet mechanisms offer several other advantages. Straightforward valve action produces a very rapid response rate, enabling precise control of timing and flow volume. In addition, the poppet provides a closed crossover, sealing the exhaust port before opening to flow. This prevents a transitional state from one function to the next, providing the operator precise control between positions. Poppet valves also impose less wear on internal seals than equivalent spool valves, resulting in typical valves with rated life expectancies of more than 50 million cycles.
Manifolds are often used to provide a common source or exhaust for an array of valves. One of the most common applications is connecting a single pressure source to multiple actuators. In this configuration, manifolds are also used as common pressure sources in hospital equipment such as air beds (alternating pressure mattresses) and gas dispensing systems. Manifolds can also be used to combine the exhausts from multiple valves. One of the most common applications for this configuration is multisource sampling systems, such as those used to analyze air quality throughout a building.