Patent Application
20050284525
Not Applicable.
Not Applicable.
The present invention relates in general to fluid-control lockout valves, and, more specifically, to piloted, manually-actuated lockout valves that provide energy isolation in high capacity systems in a control-reliable manner.
Compressed fluid systems are used in many industrial settings to operate various types of pressure-controlled actuators. Pneumatic systems use air or other gasses as the working fluid. Hydraulic systems use oil or other liquids. In a typical system, air or other working fluid is compressed by a compressor and delivered to the actuators via a distribution system including conduits and valves. Some systems may cover a very large area with one or more high capacity compressors pumping compressed air or other fluid into an extensive network of delivery conduits. The network typically includes sections that can be isolated from the compressor(s) by closing certain valves known as lockout valves. This allows portions of the system to be disassembled for maintenance or other reasons.
Prior to attempting to disassemble or service a pneumatic or hydraulic system, it is necessary to ensure that the supply of pressurized fluid is removed from the point in the system being accessed and that residual pressure is released. Various safety standards and governmental requirements exist which establish that lockout of a particular portion of a system be achieved in a control-reliable manner or by a directly-operated manual valve.
Control reliability means that an extremely high confidence factor is present (e.g., near 100%) such that when an attempt is made to actuate a valve function, the function happens. According to a standard definition, control reliable devices are redundant, monitored for their performance, and they fail to a safe condition which inhibits further operation until the failure is corrected. A manual control is often required, and a mechanical locking device (such as a padlock) installed to ensure that the pressurized fluid remains shut off during machine repair or other operation.
High capacity fluid distribution systems require valves with larger port sizes and larger valve elements (i.e., poppets or spools). At larger valve sizes or higher operating pressures, the actuating force required to move the valve element between its open and closed positions could become too high for convenient manual actuation by some persons. Larger valves (such as the 27 Series poppet valves sold by Ross Controls) use pilot actuation to offset the higher forces by employing a smaller valve to control the application of pressurized fluid to actuate the larger valve. However, the pilot-actuated control valves of the prior art have not been control-reliable since they are not redundant nor monitored, and therefore, actuation of a pilot element does not sufficiently ensure corresponding actuation of the main flow-control valve. If the main valve were to stick in its open position, then high-pressure fluid could continue to flow through the valve even though the pilot valve made it appear that the flow was shut off.
The present invention has the advantage of achieving control-reliability for locking-out flow control valves that would otherwise require excessive actuation forces when using a manual shutoff. Valve redundancy, monitoring, and a “fail to safe” design yield a control-reliable confidence level for the lockout operation.
In one aspect of the invention, a control-reliable lockout valve system having an inlet port for coupling to a source of pressurized fluid and an outlet port for coupling to a downstream fluid-actuated device is provided. A double valve unit includes a pair of valve elements each controllably moving between a respective actuated position and a deactuated position to control a first flow path between the inlet port and the outlet port in response to a pilot pressure applied to the valve elements. The first flow path provides the pressurized fluid to the outlet port only if both of the valve elements are in the respective actuated positions. The double valve unit further includes an exhaust port, and the valve elements control a second flow path for coupling the outlet port to the exhaust port unless both of the valve elements are in the respective actuated positions. A pilot supply valve is provided having an inlet for coupling to the source of pressurized fluid, an outlet coupled to the double valve unit, and a manually actuated valve element for selectably applying the pilot pressure to the valve elements of the double valve unit, whereby the manually actuated valve element can be closed to isolate the valve elements of the double valve unit from the pilot pressure to lockout the valve system in a control-reliable manner. In one optional embodiment, one or more solenoid-operated valves can be connected in the pilot circuit to provide remote or automatic control of application of pilot pressure to the double valve unit.
The present invention incorporates a manually actuated pilot device with a double valve to achieve a high level of reliability. The pilot device reduces the amount of force necessary to operate the lockout valve, so that no special strength or tools are necessary to activate the lockout function. By using a double valve, control-reliability is obtained since the double valve is redundant, monitored, and if one valve fails to properly actuate or deactuate, the second valve provides the desired function. The malfunction of the one valve element is detected by performing monitoring and the user is automatically warned that a fault has occurred. As a consequence of the fault, the back-up function is no longer available so that the valve needs to be repaired before placing the system back into service.
Referring to
In order to safely perform maintenance upon machine actuator 15 or valve 16, lockout valve 13 must be closed in order to remove the source of pressurized fluid from the corresponding sub-circuit. Compressor 11 may continue to provide pressurized fluid to other sub-circuits.
A manually operated lockout valve of the prior art is shown in
The double valve unit includes crossover passages 41 and 42 which cross-couple the valve elements to provide monitoring and inhibit further operation of the double valve unit whenever either valve element fails to operate as intended. Pressure switches 43 and 44 contained in a monitor assembly 45 are coupled to crossover passages 41 and 42, respectively. Pressure switches 43 and 44 detect the actuated or deactuated positions of the valve elements, and the resulting electrical signals from pressure switches 43 and 44 are coupled to a logic block 46 to generate a warning signal when the pressure switches indicate non-matching pressures exist in the first and second crossover passages. The identity of a failed valve element can also be determined based on which crossover passage is at nominal pressure while the other crossover passage is unpressurized due to a failure. Any type of monitoring device other than the pressure switches as shown can also be used, such as monitors available from Ross Controls under the names of Cross Mirror, Ross E-P monitor, Ross L-G monitor, and Ross DS monitor.
When manual pilot supply valve 37 is deactuated in order to obtain a lock-out position and isolate a pneumatic sub-circuit, it is highly likely that at least one valve element of the double valve unit will deactuate, thereby achieving the required isolation. However, if one valve element fails to deactuate then the double valve unit will remain in a faulted condition and the valve system cannot be reopened regardless of the position of the manual pilot supply valve. By providing monitoring with the pressure switches, the faulted condition can be indicated to an operator and repairs can be made to correct the problem with the faulted valve element.
A visual pressure indicator 47 may optionally be coupled to outlet port 34 to provide a method for verifying the complete release of pressure/energy in the system. A visual indicator such as the 988H30 visual indicator from Ross Controls can be used. The pressure indicator unit has a predetermined threshold to show whether pressure is present at the outlet port at greater or less than the threshold pressure. The threshold is selected based upon safety requirements of the particular system, for example.
