Tham khảo tài liệu 'gas station construction and maintenance, petroleum systems contractor nevada and arizona_12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Simpo PDF Merge and Split Unregistered Version - http UFC 3-460-03 21 JANUARY 2003 Attachment 3 TEST PROCEDURE FOR SETTING THE PRESSURE DIFFERENTIAL CONTROL CDHS-3 . In General. The CDHS-3 control operates from a DP produced by the orifice plate on the outlet of the main valve. The orifice plate bore size is on the flange of the orifice plate. Once you identify the orifice plate bore size you can compute its DP at a given flow rate Figure . By knowing this DP testing becomes a matter of producing the DP across the diaphragm of the CDHS-3 control and adjusting the control until it trips. For this method you add shutoff valves in the CDHS-3 sensing lines to shut off the fuel supply then add external pressure equal to that produced by the differential across the orifice plate and make the adjustment. Figure shows the location of the shutoff valves and the equipment needed for the adjustment. Figure . Flow Chart. 143 Simpo PDF Merge and Split Unregistered Version - http UFC 3-460-03 21 JANUARY 2003 Figure . Shutoff Valves. . Installing Valves. Shutoff valves 1 and 2 are in the high- and low-pressure sensing lines between the orifice plate and the CDHS-3. Install valve 3 on a T in the high-pressure sensing line on the CDHS-3 side of valve 1 to connect the air pump and pressure gauge. Install valve 4 on a T in the low-pressure sensing line to vent the low-pressure side of the diaphragm to the atmosphere. Now the excess flow control may be set without flowing fuel through the system. . Set DP. To find the correct DP on the flow chart in Figure move to the right across the bottom line of the chart to find the flow rate gallons per minute at which your system typically operates then move vertically towards the top of the chart until the gallon-per-minute flow line intersects the line drawn from the orifice bore size. From this intersection follow the line to the left of the chart and read the DP in psi. .
