Fluid, gas regulating valves offer precise, steady control for various medical, industrial, and commercial applications.
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)
TYPICAL APPLICATIONS
Air beds – Also known as medical air mattresses, play a vital role in preventing or treating serious ailments related to extended bed rest, such as pressure sores and skin shearing. Beds consist of an array of inflatable cells that can be alternately inflated or deflated to prevent any single part of a patient’s body from being continuously pressed into the mattress. LP/HV valves control the air flow into the cell arrays.
Oxygen concentrators – Provide safe, low pressure source of oxygen for healthcare and industrial applications. They extract oxygen from the atmosphere using zeolite minerals which absorb large quantities of nitrogen at high pressure. An oxygen concentrator uses an air compressor to alternately pressurize two cylinders filled with zeolite pellets to about 20psi, during which time the zeolite becomes saturated with nitrogen. As the nitrogen in the cylinder is fully absorbed, the valve to the compressor closes and a second valve opens, allowing the oxygen enriched gas to flow through a pressure equalizing reservoir and onto the patient. When the pressure drops to the point where the zeolite begins to release its nitrogen charge, the LP/HV valve to the reservoir closes and the tank can vent the desorbing nitrogen gas to the atmosphere. Once the desorbtion is complete, the tank is purged, re-pressurized and the cycle repeats. Alternating the absorb/desorb cycle between the two cylinders maintains a steady stream of oxygen. Some oxygen concentrator systems use an on-demand delivery system to reduce the amount of gas they must produce. In these units, another LP/HV valve meters oxygen flow to the patient. LP/HV valve’s low-power characteristics reduce the load on the batteries of portable concentrators and backup power systems for stationary systems.
Fluid-flow – LP/HV valves can provide reliable, efficient, and cost-effective control of fluid flow in a variety of applications.
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 . 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 1). 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.
