APTech AP74B User Manual
Operation manual flow switches, A. general information, B. installation
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Napa, CA 94558
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FAX: (707) 259-0117
www.aptech-online.com
Manual 15000002 Rev 2
Page 1 of 4
Operation Manual
Flow Switches
(Models AP74 and AP74B)
A. General information
The AP74 and AP74B flow switches are used in gas delivery systems to signal an increase in
flow above a trip point. The signal is transmitted by a closed or open electrical contact from a
reed switch. The signal is typically monitored by a controller, which closes an isolation valve in
the gas delivery system when an “excess flow” signal is received. Many models are available
with different operating characteristics (pressure ratings, trip points, etc.) and porting
configurations.
Refer to the appropriate catalog data sheet for specific product information.
Product Note PN 423 is the application guide for flow switch sizing, installation, and
troubleshooting. It is available on the AP Tech website (www.aptech-online.com). Click the
“Tech Briefs” tab at the top of the page and scroll down to “Product Notes”.
To assist in flow switch selection, an online calculator tool is also found on the website. Access
the tool in the lower left corner of the home page by clicking the tab marked “Flow Trip Point
Calculator”. Enter gas and pressure conditions and read the calculated trip points adjacent to the
flow switch models.
B. Installation
1. Prior to installation, verify that the operating characteristics of the flow switch as
described below are appropriate for the system in which it will be installed.
a. Verify the materials of construction are compatible with the intended process gas.
b. Verify the pressure and temperature ratings are acceptable for the intended application.
c. Verify that the trip point of the flow switch is appropriate for the application.
d. Verify that the flow switch will be used in gas service only.
2. Inspect the flow switch to determine the flow path through the device and how the flow
switch will need to be installed in the system.
a. The AP74 has a flow arrow on the model number label on the body that indicates the forward
flow direction.
b. The AP74B has a flow arrow on the model number label on the body of the switch in the
bypass line that indicates the forward flow direction. The forward flow direction in the
AP74B main line is parallel to the flow in the bypass line.
3. Ensure there are no sensitive electronic devices near the intended installation location.
The flow switch contains a strong magnet that could adversely affect these devices.
Ensure there are no strong magnets near the AP74 or AP74B. A strong magnet can
Document Outline
- A. General information
- B. Installation
- 1. Prior to installation, verify that the operating characteristics of the flow switch as described below are appropriate for the system in which it will be installed.
- a. Verify the materials of construction are compatible with the intended process gas.
- b. Verify the pressure and temperature ratings are acceptable for the intended application.
- c. Verify that the trip point of the flow switch is appropriate for the application.
- d. Verify that the flow switch will be used in gas service only.
- 2. Inspect the flow switch to determine the flow path through the device and how the flow switch will need to be installed in the system.
- a. The AP74 has a flow arrow on the model number label on the body that indicates the forward flow direction.
- b. The AP74B has a flow arrow on the model number label on the body of the switch in the bypass line that indicates the forward flow direction. The forward flow direction in the AP74B main line is parallel to the flow in the bypass line.
- 3. Ensure there are no sensitive electronic devices near the intended installation location. The flow switch contains a strong magnet that could adversely affect these devices. Ensure there are no strong magnets near the AP74 or AP74B. A strong magnet...
- 4. Install the flow switch using the appropriate method described below.
- 5. Connect switch signal wires to appropriate controller as described below (see also section C. Precautions and Applications).
- 6. After installation, verify the following to ensure correct operation.
- 7. After installation, perform a helium leak test of all face seal connections and welds per standard industry practice (reference SEMI standard F1).
- 8. After installation, perform a nitrogen gas flow test to verify that the switch trips sending a signal to the controller and resets when flow is shut off.
- 1. Prior to installation, verify that the operating characteristics of the flow switch as described below are appropriate for the system in which it will be installed.
- C. Precautions and Applications for Wiring Reed Switch
- When a reed switch is to be connected to an inductive load or a load where surge current or a rush current flows, the following contact protection circuits are required.
- 1. Inductive loads – when an electromagnetic relay, electromagnetic solenoid, or electromagnetic counter, which has inductance, is installed as a load in a circuit, the energy stored in the device will cause an inverse voltage when the reed contacts o...
- 2. Capacitive loads – when a capacitor is provided in series or in parallel with the reed switch contacts in a closed circuit, the in rush current, which flows at the time of charge and discharge of the capacitance, will cause deterioration of the ree...
- 3. Lamp loads – when a lamp load is used with the reed switch, the in rush current can cause deterioration of the reed contacts. The follow two figures show examples of protection circuits.
- 4. Wiring capacitance – when wiring a load and reed switch over a long distance, electrostatic capacitance arising from the cable can influence the reed switch contact and an inductor LS should be installed. The inductance (LS) value depends on the l...
- D. Operation