Haskel 28791-4 Air Pilot Switch
Description:
An air pilot switch is a pressure switch. These units produce a pneumatic signal up to 150 psi at any sensing pressure within their adjustment range. The signal valve may be piped normally-open, normally-closed, 3-way or 2-way (depending on the model).
All models use a 2-position poppet-type air signal valve which is shifted from its normal position by a rod from the sensing end which first must overcome an adjustable force spring (styles “A” and “C”) or an air-regulated dome loader (style “B”).
Applications:
- Direct automatic start/stop control of any Haskel pump, gas booster, air amplifier or indirectly to the drive of any pump or compressor sensing either output or suction (schematics 1 & 2)
- Valve actuators (schematic 5)
- Pneumatic alarm signals
- Replace an explosion-proof pressure switch in hazardous applications (schematic 6)
Haskel 28791-4 Air Pilot Switch Specifications:
- Style: C
- Description: Internally-Adjusted Air Pilot Switch
- Max Sensing Pressure: 10,000 psig
- Air Valve: 2-Way N.O.
- Adjustable Range (normally-open): 2000-8500 psig (factory setting at no charge; specify if increasing or decreasing)
- Length: 6-1/8″
- Diameter: 1-3/8″
- Air Ports: 1/4″ FNPT Out; 1/8″ FNPT In
- Sensing Port: 1/4″ FNPT
Notes:
- SAFETY: When using N.O. models to limit pump output pressure, also include a backup relief valve.
- AIR VALVE: Materials are Aluminum, Stainless Steel, Bronze and Buna; suitable for air and most gases. Modification available for sour natural gas to meet NACE SPEC. MR-01-75.
- SENSING SECTIONS: Materials are Stainless Steel, PTFE and Buna; suitable for most liquids and gases. Modification available for sour natural gas and fire-resistant hydraulic fluids.
Deadband note:
Users often try to compare the on/off actuation of the air signal with the action of an electrical switch. They are not really comparable. The air switch has no “snap-over” mechanism required with an electrical switch to prevent arcing. Therefore, “on” or “off” before or after a dead tight seal condition can be quite subjective. In other words, if the air pilot switch is turning on a device that only requires a miniscule leak to start, it will start much sooner than some other larger device that may need a flow of air to start. Therefore, it is not possible to publish a precise deadband data such as that available for most electric pressure switches.
Style B “Remoteset” units have the lowest and most consistent deadband (5% – 10% of set pressure) because there is no heavy coil spring to compress.
Style A and C may vary from 5% to as high as 40%, depending on model and the application details.
In some applications, a wider than normal deadband is needed. Schematic 4 illustrates how to provide this with two air pilot switches and a simple 2-position air valve.
Product Catalog: High Pressure Valves and System Components Catalog
