Overview

The HTAF2 is a “Smart” Header Tank Automatic Fill Control Relay. This device automatically keeps the aircraft header tank full without over stressing any fuel pumps. It can be operated manually (without any fuel sensors mounted in the header tank), or automatically, with one or two optical fuel sensors mounted in the side of the header tank or the your sight tube plumbing. The fuel sensor used for the HTAF2 is a very reliable optical fuel level sensor (optional) that can be easily installed in the header fuel tank. If the user is not able to install a fuel sensor in the header fuel tank, the HTAF2 can be wired to a normally open push button switch to activate the timed pumping. The unit also has a relay output that can be used for a light to indicate when the fuel in the header tank is low. The light will flash indicating when there are any system malfunctions detected. This detection of low fuel is also damped so that it does not falsely indicate low fuel in the case of sloshing fuel. The system can be powered by +12V or +24V electrical systems.

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Features

• Smart Operation
• Automatic Fuel Pump Turn On & Shutoff
• Easy Installation
• User Selectable Pump Time Period (0 to 10 Minutes)
• Operation Manual, One, or Two Sensor Modes
• New Design Minimizes Wiring
• Reliable Optical Fuel Sensors
• Pump-Up Completed Signal
• Sloshing Fuel Will Not Affect Operation
• Header Tank Low Fuel Indication (With 1 or 2 Sensors)

Specifications

• Input Power: 12 to 14Vdc or (24 to 28Vdc), 0.1A max.
• Enclosure: 3.5" x 2.25 x 1.25" (89mm x 57 x 32mm)
• Fuel Sensor Mounting: 1/4NPT
• Weight: 3.0oz. (93g), 3.3oz. (103g) with sensor
• Relay Contact Outputs: 10A max.

Operation

Two Sensor Operation (fully automatic)

• When low fuel is detected in the header fuel tank by the lowest sensor, the HTAF2 will pump fuel into the header tank until the highest sensor detects a full level. It will then, quit pumping.

One Sensor Operation (automatic start, with a timed stop)

• When low fuel is detected in the header fuel tank by the lowest sensor, the HTAF2 will pump fuel into the header tank for a customer specified time period (0 to 10 minutes). It will then, quit pumping.

No Sensor Operation (pilot initiated manual start, with a timed stop)

• The HTAF2 is normally used with very reliable optical fuel level sensors mounted in the header tank. If the user is not able to install any fuel level sensors in the header fuel tank, the HTAF2 can be set up so the pilot may manually activate the HTAF2. It will then pump for a customer specified time (0 to 10 minutes), then quit.

The HTAF2 also has two relay outputs that can be used for a remote or pilot light indications. One output is a low fuel indication. The low fuel relay output is damped so that it does not falsely indicate low fuel in the case of sloshing fuel. This relay output is also used to indicate system errors if connected to an indicator light, it flashes the light with different timing to indicate what failure occurred. The other output is triggered when the fuel pump is active.

Installation

• If the user is not able to install a fuel sensor in the header fuel tank, you have two options:
• Option #1
• • If you have a fuel sight tube available or you can fabricate one for the header tank, you might be able to install the sensors in the lines going to or from the sight tube. You can install a “T” connector in line and install the sensors in that connector.
• Option #2
• • If you do not have a fuel sight tube or cannot install one, there is another option. You may implement a manual start of the fuel pump and a user specified timed pump finish. The HTAF2 can also be set up so the pilot may manually activate the HTAF2. This can be accomplished with a normally open switch (NO) connected between terminals 4 and 1 (common). Pressing this switch once simulates a low fuel condition starting the HTAF2. This switch can be installed on the instrument panel. If you choose to use option #2, it will operate exactly like the one sensor connection. The only change is that the operator will have to initiate the pumping instead of relying on a low fuel sensor.
• Selecting A Pumping Time-(for NO sensor or ONE sensor operation)
• • If the HTAF2 system does not utilize any sensors, or only the start sensor, you may manually select a pumping time. This can be accomplished by installing a permanent resistor (or variable potientiometer) across input terminal 2 to common. The “approximate” resistance value should be selected from the following table. You may have to vary it a bit to get an exact time if you desire. To ensure that you have selected and installed the proper resistance value, you may measure the voltage at terminal 2 to common and compare it with the table below.
• Malfunction Warning Alarm
• • The HTAF2 has two built-in malfunction alarm features. They are both indicated by a toggling or flashing of the Fuel Detect Relay output. If you want to view this indication, you should connect a light or LED indicator to this relay output and install it in the cockpit.
• Condition Fast Flash (every 0.5 seconds)
• • It condition indicates when:
  • The Start Sensor goes high (+5V) indicating that the unit should start pumping AND The Finish Sensor output is already low (zero volts) indicating that the tank is already full.
  • This condition indicates that one or both sensors are not functioning properly. There may be several causes of this condition and is left up to the user to troubleshoot it.
• Condition Slow Flash (every 2 seconds)
• • It condition indicates when:
  • The Start Sensor goes high (+5V) indicating that the unit should start pumping AND pump has been pumping for 30 seconds.
  • This condition indicates that one or both sensors are not functioning properly. It might also mean that the fuel pump is not pumping an adequately volume to get the fuel level above the start sensor. There may be several causes of this condition and is left up to the user to troubleshoot it.