This FAQ covers the most common questions engineers ask when evaluating, sizing, and specifying PFS Series pneumatic spring-applied caliper disc brakes for industrial applications.
Understanding Spring-Applied Brakes
What is a pneumatic spring-applied brake?
A pneumatic spring-applied brake is a fail-safe caliper disc brake that uses compressed air to release (not engage) the braking mechanism. Internally, one or more Belleville disc spring stacks store energy when compressed air pushes the brake piston away from the disc rotor.
When air pressure drops or is removed, that stored spring energy releases, driving the piston and friction pad back against the rotor and engaging the brake automatically.
What does "fail-safe" mean in a brake context?
A fail-safe brake is designed to engage automatically when something goes wrong — a power outage, an air supply failure, an emergency shutdown signal. Rather than relying on active input to stop or hold a load, the brake's default state is engaged. Air pressure is used only to release it during normal operation.
This matters most in applications where uncontrolled motion during a power or air loss event poses a safety or equipment risk.
When should I specify a pneumatic spring-applied brake?
Specify a spring-applied brake when the consequence of uncontrolled motion during a power or air loss event is unacceptable.
Spring-applied brakes are the right choice when:
- The load must be held in position during a power or air failure
- Emergency stopping without an active command is required
- Regulatory or safety standards require a fail-safe mechanism
- The application involves suspended loads, elevated positions, or linear motion that could cause harm if unsupported
What are the primary use cases for Branham PFS Series brakes?
PFS Series brakes are designed for emergency stopping and position holding. They are intended for intermittent use in these roles — not for continuous or cyclic braking applications.
Within those two functions, PFS brakes are used across a wide range of rotary and linear industrial applications.
Applications
What industries and equipment types commonly use pneumatic spring-applied brakes?
PFS Series brakes are specified across a broad range of industrial applications:
- Elevator safety systems — immediate engagement on power loss, reliable holding across varied load conditions
- Overhead gantry cranes — precise load holding in any position, with multiple mounting configurations and weather-resistant options for outdoor installations
- Robotics and automation — compact form, high torque-to-size ratio, and easy integration with control systems
- Rotary indexing equipment — accurate stop positioning, rapid cycling capability, consistent torque output
- Wind turbines (up to 50kW) — all-weather operation, low-maintenance design for elevated installations
- Mining and bulk material handling — sealed construction for contaminated environments, high torque capacity, emergency stopping on inclined conveyors
- Port and marine applications — marine-grade materials and coatings, compatibility with existing shipboard pneumatic systems
- Conveyor systems — emergency stop and position holding for equipment with rotating components
- Off-highway parking brake applications — including utility vehicles and equipment with cable reels or other controlled-motion systems
Can PFS brakes be used outdoors or in harsh environments?
Yes. Standard PFS Series construction uses cast aluminum housings with hardcoat treatment on both interior and exterior surfaces, providing solid resistance to humidity, moisture, and general industrial contamination. It should be noted that conditions where moisture or contaminants accumulating on the rotor or friction pads will adversely impact the rated braking force.
For more demanding environments, optional upgrades include:
- Viton seals for chemical or solvent exposure
- Electro-nickel plating for additional corrosion resistance
- Stainless steel hardware for marine or high-humidity applications
For port, marine, outdoor gantry, and similar applications, these options provide the protection needed for long service life in corrosive conditions.
Can PFS brakes be used on linear applications?
Yes. When the application is linear rather than rotary, the tangential force rating of the selected PFS model is used to determine maximum load capacity — rather than calculating braking torque from disc diameter.
Most PFS Series models can also be mounted directly on a linear rail or plate, making them a practical option for linear axis holding and emergency stop applications.
Sizing and Selection
How do I size a PFS brake for my application?
Start with understanding your application type:
- Dynamic stopping (rotary): Account for the weight of the rotating mass, the radius of gyration based on shape, the RPM at engagement, and the required stopping time.
- Static holding (rotary): Determine the torque required to hold the load in position, then select a model and disc diameter combination that meets or exceeds that value.
- Linear applications: Use the brake's tangential force rating directly against your load requirement.
Once you have the required torque or force, apply a 20% safety margin to ensure adequate braking force is available across the range of operating conditions. Then select the PFS model and disc diameter that meets the resulting target.
How is braking torque calculated?
Braking torque is calculated using the formula:
Torque (in·lb) = Tangential Force (lb) × Braking Radius (in)
Braking radius varies by model and disc diameter.
Braking radius tables for each model are provided in the PFS Series product guide.
How is tangential force calculated from clamping force?
Tangential Force (lb) = Clamping Force (lb) × 0.45
The 0.45 figure is the coefficient of friction for the standard non-asbestos friction pad material used across the PFS Series. This calculation reflects the force at zero pad wear — as friction pads wear over time, tangential force decreases. Size with this degradation in mind, and use the 20% safety margin to maintain adequate braking force across the pad's service life.
How does friction pad wear affect braking performance?
As friction pads wear, the spring stack extension changes, which reduces the clamping force — and therefore the tangential force and available braking torque. This is a predictable, gradual effect that is charted for all PFS Series models.
Make sure not to size a PFS brake to the minimum required torque at zero pad wear. Apply the 20% safety margin during selection, and establish a regular pad inspection schedule so pads are replaced before performance degrades below acceptable levels. Excessive wear may also indicate the brake is undersized for the application.
Which PFS model is right for my application?
Nine models span a wide range of torque requirements, disc diameter constraints, and force levels:
- PFS38: 216 lb tangential force, single spring stack, unlimited disc diameter — entry-level model for lighter-duty holding and stopping applications
- PFS47: 465 lb tangential force, single spring stack, unlimited disc diameter — mid-range model for moderate torque requirements
- PFS200: 929 lb tangential force, dual spring stacks — for disc diameters up to 16 inches
- PFS200SUL: 929 lb tangential force, dual spring stacks — same force as PFS200 but configured for disc diameters above 16 inches
- PFS200UL-EP: 929 lb tangential force, extended pad configuration — from 12 inches to unlimited disc diameter, with significantly more wearable pad material for longer service intervals
- PFS400F: 1,859 lb tangential force, dual spring stacks — for disc diameters from 12 inches to unlimited
- PFS400F-EP: 1,859 lb tangential force, extended pad configuration — same force range with extended pad life
- PFS520: 6,419 lb tangential force, aluminum construction, quick-change pad feature — requires 20-inch or larger discs, suited to high-torque industrial applications
- PFS522: 12,236 lb tangential force, aluminum construction, quick-change pad feature — the highest-force model in the series, also requires 20-inch or larger discs
All models release at 85 PSI except PFS520 (75 PSI) and PFS400F/400F-EP (100 PSI). Contact us for selection assistance if your application falls at the boundary of multiple models.
Model Specs and Configuration
What models are available in the PFS Series?
The PFS Series includes nine models designed to cover a broad range of torque output, disc size, and environmental requirements: PFS38, PFS47, PFS200, PFS200SUL, PFS200UL-EP, PFS400F, PFS400F-EP, PFS520, and PFS522. Full specifications for each are available in the PFS Series product guide.
What is the difference between a standard model and a ‘UL’ model?
The standard model is designed for a specific range in disc diameter. The ‘UL’ or Unlimited model is designed for a specific disc diameter and larger. It can be used in a linear application. Some standard models such as the PFS38 can be used linearly.
What release pressure is required?
Release pressure requirements vary by model:
- 85 PSI: PFS38, PFS47, PFS200, PFS200SUL, PFS200UL-EP, PFS522
- 75 PSI: PFS520
- 100 PSI: PFS400F, PFS400F-EP
Maximum operating pressure across the series is 100 PSI (6.9 Bar). General operating range is 70 to 120 PSI.
What disc thicknesses are supported?
Standard models accommodate disc thicknesses of 5/32", 1/4", 3/8", 1/2", 5/8", 3/4", 1.0", and 1-1/8". Fitment for other thicknesses, including metric sizes, is possible — consult our team for non-standard requirements.
What disc diameters are compatible with each model?
Disc diameter compatibility varies by model:
- PFS38, PFS47: Unlimited disc diameter
- PFS200: Designed for disc diameters up to 16 inches
- PFS200SUL, PFS200SUL-EP, PFS400F, PFS400F-EP: From 12 inches to unlimited
- PFS520, PFS522: Require disc diameters of 20 inches or larger
What are the standard construction features?
All PFS Series models share the following standard construction:
- Cast aluminum construction
- Hardcoated housings on both interior and exterior surfaces
- Non-asbestos friction pad material
- Replaceable friction pads
- Buna-N seals
- Float mount
- Belleville disc spring stack(s)
- 0.45 coefficient of friction
- 100 PSI (6.9 Bar) maximum pressure
What optional upgrades are available?
Optional features available across PFS Series models include:
- Viton seals (for chemical resistance or higher-temperature environments)
- Electro-nickel plating (for additional corrosion protection)
- Stainless steel hardware (for marine and high-humidity applications)
- Non-standard disc thickness fitment (consult factory)
Can PFS brakes be mounted on a linear rail or plate?
Yes. Most PFS Series models can be mounted on a linear rail or plate, in addition to standard rotary disc applications. This makes them suitable for linear axis holding and emergency stop functions without requiring a separate brake type.
Where can I find CAD drawings?
3D CAD drawings for all PFS Series models are available for download on our website. You can configure your CAD files on each product page.
Maintenance and Serviceability
What maintenance do PFS Series brakes require?
PFS Series brakes are designed for low maintenance. Key items to monitor during regular inspection:
- Mounting orientation: Surface of the pads should be parallel to the disc to prevent uneven wear
- Pad wear: Watch for uneven or excessive wear; replace pads before disc damage occurs. Excessive wear may also indicate the brake is undersized
- Leaks and corrosion: Two of the most common maintenance issues — address early to prevent performance degradation
- Full retraction: Verify the spring is fully retracting the brake from the disc during normal operation; corrosion or debris can interfere with retraction and cause drag
- Fittings and fasteners: Vibration can loosen fittings over time — check bolt tightness and pad-securing screws as part of routine inspection
- Guide pins: On floating (single-sided) caliper models, keep guide pins and brackets clear of debris to ensure the caliper can center itself properly against the disc
How do I know when to replace friction pads?
Monitor for uneven or excessive wear relative to the pad wear curves in the PFS Series product guide. Pads must remain thick enough to apply adequate clamping force without allowing metal-to-metal contact with the disc. Replacing pads on a scheduled basis — rather than waiting for visible failure — is the most reliable approach to maintaining consistent braking performance.
If pads are wearing unusually fast, verify the brake is correctly sized for the application. Rapid wear can indicate the brake is undersized or being used outside its intended intermittent duty cycle.
Ordering and Support
What is the standard lead time?
Most sizes are 1-week standard lead time for smaller quantities. Larger models such as the PFS520 or PFS522 will need to be verified with the factory.
Can PFS brakes be customized?
Yes. Custom modifications are available for higher-volume orders. Options range from straightforward changes — such as repositioning mounting holes or accommodating non-standard disc thicknesses — to more complex designs, such as models that release at lower pressure or provide higher torque output than the standard lineup.
How do I order or get application support?
- Phone: 1-800-428-1974 (U.S./Canada) or 715-426-2000 (local)
- Email: AskWCB@wcbranham.com
- Website: www.wcbranham.com
