836 Pressure Controls

836 Pressure Controls Selection Guide

Overview

The Allen-Bradley 836 Electromechanical Pressure Controls manufactured by Rockwell Automation are designed to monitor and control the operating parameters of diverse hydraulic and pneumatic industrial systems. In control applications, they maintain predetermined system pressures within preset high and low values. In monitoring applications, they monitor the system pressure between a low and high value, signaling whenever a preset pressure limit is exceeded.

As such, these pressure controls are helpful in detecting unusually high operating pressures of fluids to help safeguard machines and operators and improve industrial processes and systems. Also, they may be used in detecting low operating pressures to protect expensive industrial equipment and machinery from loss of lubrication and coolants.

Their high-quality design and ruggedized components provide a long service life with oil, water, non-corrosive liquids and gases, air, vapors, and several corrosive gases and liquids. Essentially, 836 Pressure Controls are designed and built for a comprehensive range of industrial applications. Typical applications include:

Vacuum conveying systems
Monitoring high and low pressures
Low-pressure alert
High-pressure alert
Air compressors
Control of liquid levels
Compressed air monitoring systems

Key Features

Ruggedized, compact design
A relatively frictionless and straight in-line construction that provides precise and consistent operation despite the mounting angle of the 836 Pressure Control
Includes stainless steel and copper alloy bellows
Available in various types of enclosure designs and ratings, including Open type(for panel mounting), NEMA Type 4X, NEMA Type 4 & 13, NEMA Type 1, NEMA Type 4 & 13, and 7 & 9 Combination Enclosures
Available with several contact blocks
Provides customized and standard refrigeration controls
Adjustable operating pressure, ranging from 30-inch Hg vacuum to 900 psi (Pounds per square inch)
Adjustable differential pressure, ranging from 0.2 psi to 125 psi
Independently adjustable reset and trip pressure settings
1/4-inch N.P.T.F. tapered thread and 7/16-20 S.A.E. straight thread connections

How Do Bulletin 836 Pressure Control Units Operate?

The Allen-Bradley 836 Pressure Controls are designed to respond to pressure changes in hydraulic (oil or water) or pneumatic (gas or air) systems by opening or closing electrical circuits. The diagram below shows a simplified mechanical structure of a typical Bulletin 836 Pressure Control, which can help us better understand the theory of operation of these controls.

The system’s pneumatic or hydraulic pressure gets connected to the 836 Pressure Control at its pressure connection point and is directly applied to the actuator. As the system pressure increases, the bellows actuator exerts a substantial force on the control’s main (primary) spring. Once the applied force overcomes the primary spring’s threshold force, the spring transfers the linear or non-linear motion generated by the bellows to the contact block, which causes the housed contacts to activate – this is known as trip pressure setting. Hence, the trip setting can be defined as the higher pressure value at which the pressure control’s contacts change from their usual state to an activated state.

As the system pressure reduces, the primary spring retracts, activating the secondary spring (differential blade spring), returning the actuated contacts to their usual state – this is known as reset pressure setting. As such, reset setting can be defined as the set lower pressure value at which the pressure control’s contacts return to their usual state.

Note: Adjusting the force of the primary spring determines the position where the contacts will trip. While adjusting, the force of the secondary spring (differential blade) determines the position in which the contacts are going to reset.

Allen-Bradley pressure controls are built to easily adjust the reset and trip pressure settings to help reduce installation time. Standard 836 Pressure Controls are calibrated at the minimum differential pressure and maximum operating pressure range from the factory. However, these factory settings can be modified to the specific requirements of a given application by following this two-step process:

Step 1 – Trip Setting Adjustment: You can modify the trip setting by adjusting the control’s operating range adjustment screw. To reduce the trip setting value, turn the screw counterclockwise. To increase the trip setting value, turn the screw clockwise. The approximate value of the trip setting is displayed on the trip-indicating scale.
- Note: Adjusting the operating range screw modifies the reset and trip pressure settings in nearly equal increments.
Step 2 – Reset Setting Adjustment: The reset setting is modified by adjusting the control’s differential adjustment screw. To increase the differential pressure setting, turn the screw counterclockwise. To reduce the differential pressure setting, turn the screw clockwise.
- Note: Turning the differential screw hardly affects the trip setting.

How to Select the Right Bulletin 836 Pressure Control Unit

When selecting a Bulletin 836 Pressure Control for a given type of pressure control application, consider the following:

1. Adjustable Operating Range

This is defined as the total span in which the contacts of an 836 Pressure Control can be adjusted to trip and reset. Check that the specified operating range of the Bulletin 836 Pressure Control you intend to select can effectively meet your application’s requirements.

2. Adjustable Differential

This is the pressure difference between the calibrated trip and reset values. Check if the recommended minimum and maximum differential pressure values will suffice the needs of your pressure control application. Minimum differential is achieved when the differential pressure of the Bulletin 836 Pressure Control is calibrated to the lowest possible pressure variation between the reset and trip settings. Maximum differential is achieved when the differential pressure of the Bulletin 836 Pressure Control is calibrated to the widest possible pressure variation between the reset and trip settings.

3. Maximum Occasional Surge Pressure

Pressure surges or transient pressures, commonly called “water hammer,” are short-lived pressure waves occurring in piping networks transporting fluid due to an abrupt change in the flow velocity, for example, when a flow-control valve is opened or closed too rapidly. They usually occur during the shutdown and startup of industrial machinery or systems.

The higher-than-usual pressure generated by a pressure surge can cause considerable damage to any pressure control system that is not designed to put up with such stresses. Therefore, ensure that you check the specified maximum value of the surge pressure applied to the bellows actuator of the 836 Pressure Control you intend to select without damaging it.

4. Maximum Line Pressure

This is the maximum sustained pressure that may be applied to the bellows actuator of an 836 Pressure Control without causing irreversible damage. Ensure that your application’s system pressure (maximum) does not exceed the recommended maximum line pressure of the 836 Pressure Control you intend to select. It is also worth noting that a Bulletin 836 Pressure Control unit should not be cycled at maximum line pressure.

5. Type of Pressure Media

Allen-Bradley 836 Pressure Controls can control many different kinds of pressure media, including hydraulic fluids, air, water, and various other types of liquids and gases.

The maximum system pressure and pressure media will help determine the type of bellows actuator (copper alloy or stainless steel) for your pressure control application. Therefore, ensure that you select a Bulletin 836 Pressure Control whose bellows actuator is compatible with the pressure media employed in the intended application. For example:

Copper Alloy internal and external bellows actuators are compatible with water, air, non-corrosive gases and liquids, and hydraulic fluids.
Stainless Steel (Type 316) external bellows actuators are compatible with water, air, non-corrosive gases and liquids, hydraulic fluids, corrosive liquids, and corrosive liquids.

6. Pressure Connection

Establish the type of pressure connection you will require in your application and select a Bulletin 836 Pressure Control unit that can be configured for that connection. Essentially, Allen-Bradley 836 Pressure Controls are available with the following pressure connections:

7/16-inch -20 SAE flare thread for a 1/4-inch copper tubing
1/4-inch N.P.T.F. Internal Pipe Thread
3/8-inch N.P.S.F. Internal Pipe connection (available in only 836-C1 and 836-C1A pressure controls)

7. Enclosure Type

Since the Bulletin 836 Pressure Controls are built for industrial applications, be sure to select a pressure control whose enclosure design and rating can enable it to withstand harsh industrial environments and function properly even under extreme operating conditions (i.e., very high and low temperatures, extreme humidity levels, presence of dust and debris, excessive vibration levels, etc.).

Allen-Bradley 836 Pressure Controls are available with the following enclosure types:

Open Type: This enclosure includes vents that allow cooling air to flow through the pressure control. It also provides adequate mechanical protection to the pressure control. It is well suited for applications without unusual exposure to dampness or dust particles.
Type 1: This is a general-purpose enclosure type built for indoor use. It protects against indirect splashing, light, dust, and falling dirt. However, it’s not dust-tight. As such, it’s primarily used to prevent incidental contact with the enclosed pressure control.
Type 4X: This enclosure is fabricated from corrosion-resistant material, such as stainless steel, to protect against corrosive agents like salt spray. It also provides a superior degree of protection against splashing water, windblown dust, snow, rain, hose-directed water, and sleet. It’s suitable for indoor or outdoor applications, including offshore pressure control applications. Most Type 4X enclosures have welded couplings, insulation retainers, pre-punched holes, view windows, and a unique gasket to protect against solid and liquid ingress.
Type 4 &13: This enclosure includes an oil-resistant gasket. It protects oil, water, and dust. Hence, it can be used in areas regularly hosed down or in very oily or wet operating conditions. For outdoor applications, the enclosure should be used together with a drip shield.
Type 7 & 9 and 4 & 13 Combined Enclosure: This enclosure is provided with an O-ring seal and a special gasket to prevent dust, hazardous gases, moisture, and other fluids from ingressing into the enclosed pressure control. It is primarily rated for use in environments classified as:
- CLASS I locations: Groups C and D
- CLASS II locations: Groups E, F, and G
- CLASS III locations Note: Enclosures rated as Type 7 & 9 are not constructed to prevent moisture ingression.

8. Device Style

836 Pressure Controls are available in different styles to meet various general industrial applications. Operating and differential pressure ranges, maximum occasional pressure surge, maximum line pressure, appropriate enclosure types, pressure connections, and the compatibility of the bellows actuator with various kinds of pressure media are usually provided in the specification sheets of Allen-Bradley 836 Pressure Controls to help in the selection of the proper pressure control. Therefore, to select a device style that can best meet your pressure control needs, be sure to review its specified features and operating parameters properly.

Available Allen-Bradley 836 Pressure Controls are of three types/styles, namely:

a) Bulletin 836 Style A

The Bulletin 836 Style A Pressure Control features the following:

Small size internal bellows made of copper alloy
Adjustable operating pressure range — 30 in. Hg Vacuum to 375 psi
Adjustable differential pressure range — 2 psi to 95 psi
Occasional surge pressure — 850 psi maximum
Line pressure — 750 psi maximum
Pressure connection requires a 7/16-inch -20 SAE flare thread for a 1/4-inch copper tubing
Available in Open Type (no enclosure), Type 4 & 13, Type 1, or Type 4 & 13 and 7 & 9 combined enclosures

b) Bulletin 836 Style C - Copper Alloy External Bellows

The Style C 836 Pressure Controls are characterized by:

External bellows made of copper alloy
Adjustable operating pressure range — 30 in. Hg Vacuum to 900 psi
Adjustable differential pressure range — 0.2 psi to 125 psi
Occasional surge pressure — 1600 psi maximum
Line pressure —1300 psi maximum
1/4-inch female N.P.T. threaded pipe connection
3/8-inch female N.P.T threaded pipe connection (available with only 836-C1A and 836-C1 pressure controls)
Available in Open Type (no enclosure), NEMA Type 4 & 13, NEMA Type 1, NEMA Type 4X, or NEMA Type 4 & 13 and 7 & 9 combined enclosures

Note: Bellows actuators made of copper alloy are well suited for use in air or water and other gases or liquids that are not corrosive to the copper alloy.

c) Bulletin 836 Style C - Stainless Steel External Bellows

These 836 Pressure Controls feature the following:

External bellows made of Type 316 stainless steel
Adjustable operating pressure range — 30 in. Hg Vacuum to 375 psi
Adjustable differential pressure range — 0.4 psi to 80 psi
Occasional surge pressure — 650 psi maximum
Line pressure — 650 psi maximum
1/4-inch female N.P.T. threaded pipe connection
Available in Open Type (no enclosure), NEMA Type 4 & 13, NEMA Type 1, NEMA Type 4X, or NEMA Type 4 & 13 and 7 & 9 combined enclosures

Note: The stainless steel (Type 316) bellows actuators can be utilized on corrosive gases or liquids.

9. Standards Compliance

The Bulletin 836 Pressure Control you intend to select should be compliant with the following standards:

UL 508
UL 1604 (rated for Hazardous Locations)
UL 698 (rated for Hazardous Locations)
CSA 22.2 No. 14
IEC 529/IP2X
NEMA ICS-2

The selected 836 Pressure Control should also include the following certificates of compliance:

UL & CSA (for Standard Applications and Hazardous locations)
CE (for Standard Applications)

10. Required Accessories

If required, select the appropriate accessories for the type of Bulletin 836 Pressure Control you have chosen. These may include:

a) Pipe Adapter: Style A Bulletin 836 Pressure Controls require a 1/4-inch male-threaded pipe adapter (Catalog No. 836-N1) with a copper seating washer.

b) Contact Block Replacement Kit (Catalog No. 836-N2): This kit includes a standard contact block and instructions for use.

c) Angle Mounting Brackets: These types of brackets are required for mounting one or two Style A Bulletin 836 Pressure Controls without an enclosure (Open Type) on a mounting plate. They are available as Single Brackets (Catalog No. 836-N11) and Dual Mounting Brackets (Catalog No. 836-N12).

d) Isolation Traps: Different types of isolation traps are available for high-temperature (from 150 to 600 °F) pressure media applications (such as steam media) and for use with corrosive pressure media compatible with stainless steel (Type 316) fittings and tubing.

e) Fixed External Pulsation Snubbers: As a standard, all Allen-Bradley 836 Pressure Controls are provided with an internal pulsation snubber. However, suppose the bellows actuator of an adequately selected 836 Pressure Control being used within the recommended operating and differential range pressure values has a short service life. In that case, that’s a clear sign of the presence of extreme transient or surge pressures in the pressure control system. In such cases, fixed external pulsation snubbers should provide additional dampening whenever intense pressure surges or pulsations are present.

Generally, the use of fixed external pulsation snubbers is recommended if extreme line pressure surges occur more than eight (8) times within a 24-hour period. Available external revised surge snubbers include:

Allen-Bradley 836-N6 for use with Style A 836 Pressure Controls
Allen-Bradley 836-N7 for use with Style C Bulletin 836 Pressure Controls

f) Adjustable Element Pulsation Snubbers: These snubbers are required in pressure control systems with extreme surge pressure. They are provided with five elements of distinct porosities to allow a selectable balance between increasing the service life of the selected 836 Pressure Control and reducing its response time. Their mid-range porosity element is typically factory-mounted, while the other four porosity elements are color-coded on the ends and included in the package.

For Style C Bulletin 836 Pressure Controls, you can use the 836-N40 Element Pulsation Snubber.

g) Hardware Kits: These are required for mounting Open Type Bulletin 836 Pressure Controls in particular types of enclosures to allow ease of connecting the system’s pressure lines. Available hardware kits include Catalog No. 836-N5, Catalog No. 836-N8, and Catalog No. 836-N10.