This invention relates to a Venturi valve, and more particularly relates to a spring-loaded plunger for the Venturi valve that controls the flow of air through the Venturi valve.
Venturi valves are pressure independent flow control valves, suitable for health care and laboratory spaces that require accurate room pressurization and proper directional air flow. The valve assembly consists of a Venturi shaped outer housing and an internal plunger assembly. The plunger assembly maintains constant air flow through the valve at a given set-point or actuator position regardless of changes in static duct pressure.
A conventional Venturi valve 10 is shown in
The control arm 24 is driven by a controller (not shown) in response to HVAC system conditions and parameters. The control arm establishes a longitudinal set position or set point for the control shaft 16 of the Venturi valve 10. The set point is established with respect to the operating conditions required for the Venturi valve 10 in a particular HVAC system. After the longitudinal position of the control shaft 16 is set and as duct static pressure fluctuates, the engineered, multi-rate spring 34 inside the plunger 26 controls the movement of the plunger 26 back and forth along the control shaft 16. Movement of the plunger 26 to the left in
The spring 34 is an engineered, multi-rate spring with a particularly designed force curve. The plunger 26 of the Venturi valve 10 operates along that designed force curve of the spring 34 to ensure constant air flow through the Venturi valve 10. Under normal operating conditions, the Venturi valve spring 34 maintains an accurate level of constant air flow through the Venturi valve 10 as the plunger 26 follows the force curve of the spring 34 as designed. If the HVAC system fails and creates a pressure surge, the summation forces acting on the plunger 26 become greater than the forces experienced by the plunger 26 during normal operation. Under the circumstance of such a pressure spike, the spring 34 is over compressed, and the spring's force curve can instantaneously deteriorate. Over-compression of the spring 34 damages the spring 34, and such damage directly affects the force curve and therefore the accuracy of the operation of the plunger 26.
Engineered, multi-rate Venturi springs 34 are more susceptible to deterioration and loss of accuracy resulting from over compression because the multi-rate Venturi springs 34 use only a portion of the force curve. This means that at different loaded values on the spring 34, the force varies non-linearly. The multi-rate is achieved by a conical shape with varying pitch (the distance between each coil). During over-compression, the pitch becomes altered, and Venturi spring's force curve deteriorates rapidly. Once deterioration of the multi rate Venturi spring 34 has occurred, the spring 34 will no longer follow the designed force curve, meaning the spring will no longer respond as it did prior to the over-compression, and the Venturi valve 10 will lose accuracy.
Further, because spring design is a separate engineering discipline from HVAC design, a second party is usually employed to design and manufacture the Venturi springs 34 based on a force curve developed by the Venturi valve designer. Unless the Venturi valve designer tests to failure and discusses the spring issues with the spring designer, spring deterioration is unknown and therefore no failure preventative measures are included in the spring design.
In order to solve the problem associated with the deterioration of multi-rate Venturi springs from over compression, a hard stop is positioned on the control shaft to engage the end cap of the plunger and thereby limit the extent of the travel of the plunger. Limiting the travel of the plunger keeps the Venturi spring from becoming over-compressed during extreme conditions (pressure surges outside of normal operating range), thereby assuring that the Venturi spring will maintain its designed force curve and thereby maintaining accurate control of the air flow through the Venturi valve.
Further objects, features and advantages will become apparent upon consideration of the following detailed description of the invention when taken in conjunction with the drawings and the appended claims.
A Venturi valve 110 in accordance with the present invention is shown in
In operation, the control arm 124 is driven by a controller (not shown) in response to HVAC system conditions and parameters. The control arm establishes a longitudinal set position or set point for the control shaft 116 of the Venturi valve 110. The set point is established with respect to the operating conditions required for the Venturi valve 110 in a particular HVAC system. After the longitudinal position of the control shaft 116 is set and as duct static pressure fluctuates, the engineered, multi-rate spring 134 inside the plunger 126 controls the movement of the plunger 126 back and forth along the control shaft 116. Movement of the plunger 126 to the left in
As previously noted, spring 134 is an engineered, multi-rate spring with a particularly designed force curve. The plunger 126 of the Venturi valve 110 operates along that designed force curve of the spring 134 to ensure constant air flow through the Venturi valve 110. The designed force curve corresponds to the distance between the end cap 132 and the hard stop 136 when the spring 134 is uncompressed.
Under normal operating conditions, the Venturi valve spring 134 maintains an accurate level of constant air flow through the Venturi valve 110 as the end cap 132 of the plunger 126 follows the designed force curve of the spring 134 along the control shaft 116 from the uncompressed position of the spring 134 to the hard stop 136.
If the HVAC system fails and creates a pressure surge, the summation forces acting on the plunger 26 become greater than the forces experienced by the plunger 126 during normal operation. Under the circumstance of such a pressure spike, the plunger 126 is forced by the air flow toward the fixed piston 122 (to the left in
While this invention has been described with reference to preferred embodiments thereof, it is to be understood that variations and modifications can be affected within the spirit and scope of the invention as described herein and as described in the appended claims.
This patent application claims priority from U.S. Provisional Patent Application No. 61/804,906, filed Mar. 25, 2013, which is hereby incorporated by reference.
Number | Date | Country | |
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61804906 | Mar 2013 | US |