This FAQ covers the most common questions engineers ask when evaluating, selecting, and specifying W.C. Branham cable cylinders — including how to choose between the four available types, what limitations to consider, and how to size them for your application.
Understanding Cable Cylinders
What is a cable cylinder?
A cable cylinder is a rodless pneumatic actuator that uses an internal piston connected to an external load via steel cables routed over sheaves (pulleys) at each end of the cylinder body. When air pressure moves the piston, the cables transfer that motion to a clevis or attachment point outside the cylinder, producing linear movement without a projecting rod.
Because no rod extends beyond the cylinder body, a cable cylinder occupies the same envelope at full extension as at full retraction. A comparable rod cylinder requires nearly twice the space at full extension, which makes cable cylinders well suited to applications where available machine space is limited.
How do cable cylinders differ from band-type and magnetically coupled rodless cylinders?
W.C. Branham manufactures four types of rodless cylinders: cable cylinders, DURATRK® band cylinders, MAGTEC® magnetically coupled cylinders, and PNEU-SA® enclosed cable cylinders. Each serves a distinct set of application requirements.
Cable cylinders stand apart in three ways:
- Cost: Cable cylinders are relatively inexpensive compared to other rodless types. Steel cable costs less to produce than the extruded aluminum tube bodies used in band-type cylinders.
- Stroke length: Cable cylinders can accommodate strokes of up to 40 feet — longer than most other rodless designs — and the main cylinder body can be mounted remotely, away from harsh environments, by simply specifying longer cable lengths.
- Field repairability: W.C. Branham cable cylinders can be rebuilt in the field using repair kits, minimizing downtime in production environments. Band-type and magnetically coupled cylinders do not offer the same level of field serviceability.
The primary tradeoff is that standard (non-guided) cable cylinders require external load guidance and support — the cylinder shuttles the load, but a separate guide mechanism must maintain straight-line travel and carry the load weight. Band-type and magnetically coupled cylinders can handle direct loading without external guidance in many configurations.
What types of cable cylinders does W.C. Branham offer?
Our current cable cylinder lineup includes four types:
- Rodless cable cylinders — double-acting, applying force in both directions. The most common type, used across a broad range of industrial motion applications.
- Guided cable cylinders — a double-acting cable cylinder with an integrated guide and load-bearing support system. Self-guiding and self-supporting, eliminating the need for a separate external guidance mechanism.
- Single-acting cable cylinders — apply force in one direction only; return is handled by gravity or an external force. Designed for vertical or horizontal lifting, articulation, and counterbalancing applications.
- Linear tension cable (LTC) cylinders — designed for direct linear tensioning and counterbalancing in short-stroke applications. A cost-effective alternative to pneumatic rod cylinders where only a short stroke is required.
What applications are cable cylinders used for?
Cable cylinders are used across a wide range of industrial and manufacturing settings. Common double-acting applications include:
- Textile machinery
- Paper splicers
- Cage washers
- Packaging machinery
- Printing machinery
- Drill feeds
- Shrink wrapping
- Silk screening
- Food processing
- Material transfers
- Automotive assembly
Single-acting cable cylinders are suited for:
- Opening gates or doors
- Articulating arms
- Lifting or raising products (e.g., tires)
- Counterbalancing
LTC cylinders are used where a short-stroke tensioning or counterbalancing function is needed at lower cost than a rod cylinder alternative.
Because the cylinder body can be mounted away from the work area by specifying extra cable length, cable cylinders are also a viable choice for harsh environments. Pharmaceutical cage washers are a practical example: the cylinder body stays protected while only the cables and sheave assemblies are exposed to the washdown environment.
When should I use a guided cable cylinder instead of a standard rodless cable cylinder?
Use a guided cable cylinder when the load needs to be self-guided and self-supported rather than guided by an external mechanism. Guided cable cylinders combine a double-acting cable cylinder with a pre-engineered guide and load-bearing support system, which means you do not need to design or procure a separate linear guide.
Standard models use journal guide bearings. Linear ball bearings can be specified as an alternative for lower-friction or higher-precision applications.
If your application already incorporates an external guide rail or linear bearing system, a standard rodless cable cylinder is generally the more economical choice, since you are not paying for integrated guidance you do not need.
When should I use a single-acting cable cylinder?
Single-acting cable cylinders are designed for applications where force is required in one direction only and gravity, a spring, or another external force handles the return. They are ideal for:
- Vertical or horizontal lifting (e.g., raising a part, opening a door or gate)
- Articulating arms
- Counterbalancing
They are generally more affordable than double-acting cylinders, making them a cost-efficient choice where the application genuinely requires only one-way actuation.
What is a linear tension cable (LTC) cylinder, and when should I use one?
An LTC cylinder is designed specifically for direct linear tensioning and counterbalancing where only a short stroke is required. Unlike a standard rodless cable cylinder, which is optimized for longer linear travel, an LTC cylinder focuses on maintaining consistent tensioning force over a small range of motion.
They are a cost-effective alternative to pneumatic rod cylinders in tensioning applications because they deliver the required function at lower cost without compromising reliability.
If your application requires a longer stroke or two-directional powered movement, a standard rodless or guided cable cylinder is the appropriate choice instead.
What are the limitations of cable cylinders?
Cable cylinders are a strong fit for many applications, but there are situations where a different actuator type is the better choice:
- External guidance required (standard rodless type): A standard rodless cable cylinder does not guide or support the load. The application must include an external guide mechanism to maintain straight-line travel and carry load weight. If external guidance is not feasible, a guided cable cylinder or a different actuator type is needed.
- Not food-grade or washdown-rated: Cable cylinders are not available in stainless steel and are not designed for repeated high-pressure washdowns. Applications requiring food-grade, pharmaceutical, or high-sanitation environments should use W.C. Branham’s MAGTEC® magnetically coupled cylinders, which are available in stainless steel.
- Envelope size: The physical envelope of a cable cylinder may be larger than a comparable band-type or magnetically coupled cylinder. Verify dimensional fit early in the design process.
- Perceived as legacy technology: Because cable cylinders have been in use since the 1960s, some engineers default to newer rodless designs even when a cable cylinder would perform equally well at lower cost. The technology is mature and proven, but it is worth confirming with your team that a cable solution meets any internal standards requirements.
Sizing and Selection
How do I size a cable cylinder for my application?
The sizing process follows these steps:
- Determine available operating pressure (PSI).
- Calculate load force. For horizontal sliding applications: Load Force = Load Weight × Coefficient of Friction of the guiding mechanism. For vertical applications: Load Force = the weight to be lifted. As a general rule, oversize your calculations by 20% to account for system losses.
- Find viable bore sizes. Using the Force at Various Pressures table, identify bore sizes that produce force exceeding your calculated load force at your available PSI.
- Apply the 20% rule. Verify that your load force does not exceed 20% of the selected bore’s cable tensile strength. If it does, step up to the next larger bore.
- Set operating pressure. Calculate the required PSI: Load Force ÷ Effective Bore Area. Set the regulator at this value. Running the cylinder significantly above load pressure adds unnecessary stress to the cable and reduces service life.
- Check cushion capacity. Confirm that internal cushions can safely decelerate the load at the intended velocity by checking the inertia load table for your bore size. External adjustable shock absorbers can be added for high-speed or high-cycle applications.
- Verify stroke length. Confirm whether your stroke falls within the manual cable adjustment limit. Stroke lengths are available from a few inches up to 40 feet. Strokes beyond the manual adjustment limit require the Pressure Differential Method or automatic tensioners.
What if my required stroke exceeds the manual adjustment limit?
Two options are available:
- Pressure Differential Method: Uses the gap between actual operating pressure and maximum rated pressure to extend the stroke limit. For example, using a 1.5" bore at 41 PSI actual vs. 100 PSI rated: differential = 59%, so extended max stroke = 59% × 126" + 126" = 200.3" (16.69 ft).
- Automatic Tensioners: Each tensioner provides 2" of cable take-up. A second tensioner doubles that. Automatic tensioners are strongly recommended for vertical lifting and high-cycle applications regardless of stroke length. Mount the tensioner on the side opposite the load direction; for vertical applications, mount at the bottom.
Note: Automatic tensioners are not available for all models. Consult W.C. Branham for availability on specific bore sizes.
Options and Accessories
What is the automatic tensioner option, and when is it recommended?
An automatic tensioner maintains cable tension over the cylinder’s service life by compensating for cable stretch. It is strongly recommended in two situations regardless of stroke length:
- Vertical lifting applications (mount tensioner at the bottom)
- High cycle rate applications
Each automatic tensioner provides 2" of cable take-up. A second unit doubles that to 4". The tensioner must be plumbed to a separate, non-fluctuating pressure source set at the appropriate percentage of actual load pressure. Running above this setting does not improve performance and shortens cable life.
What is the caliper disc brake option, and how is it used?
The caliper disc brake option provides mid-stroke positioning or load deceleration at end of stroke. It is available on bore sizes 1.5" and larger (excluding 5" bore) and requires an automatic tensioner.
For position holding, use a 3-position valve with pressure applied to both cylinder ports in the center position. The brake supplements cylinder pressure for holding — it does not replace it.
Brake operating pressure formulas:
- Pressure removed before braking: Pᴮᵣ = 0.113 × Lₜᵣ × Rₛ (PSI)
- Pressure applied when braking: Pᴮₐ = 0.113 × Lₜₐ × Rₛ (PSI)
Sheave root radius values: 1.53" for 1.5" bore; 2.00" for 2" and 2.5" bores; 2.50" for 3", 4", and 2" HP bores.
What is the double stroke option?
Double stroke models produce twice the stroke and velocity of standard double-acting cable cylinders within the same cylinder body length. They also allow the main cylinder body to be mounted remotely, away from harsh conditions, while the load is actuated at a distance.
To size a double stroke application: select a double-acting cable cylinder with an automatic tensioner that produces twice the load force required. Sheave and cable sizes match the equivalent double-acting model. Cables must be proof-loaded and pre-tensioned before operation.
Are reed switches available?
Yes. Reed switch packages are available for standard rodless cable cylinders on aluminum tubing models. The RS option includes two normally open reed switches, a piston magnet, and tube clamps.
Note: Adding the RS option increases overall cylinder length by 1.62" on smaller bore models and 0.375" on mid-range bore models. Reed switches are not available on steel tubing models.
Installation and Maintenance
What is proof-loading and pre-tensioning, and why is it required?
Cable cylinders ship without correct cable tension. Before putting the cylinder into operation — after it is installed and a load is applied — the cables must be proof-loaded and pre-tensioned. This step is mandatory; skipping it significantly reduces service life.
Steel cables have two types of stretch: constructional (individual wire strands seated loosely as manufactured) and elastic. Proof-loading aligns the strands under tension to eliminate constructional stretch. Pre-tensioning removes the remaining elastic stretch.
What lubrication does a cable cylinder require?
Lubricate the cable cylinder with SAE 10 or SAE 20 non-detergent oil on a regular maintenance schedule. Periodically inspect the sheaves, cable, and gland seals for contaminants and clean as needed. Keeping the cylinder as clean as possible is the most effective way to extend service life.
When reinstalling a piston during cable replacement, use STP® 4-Cylinder Oil Treatment or equivalent on the cylinder tube interior.
How do I replace the cables on a cable cylinder?
W.C. Branham cable cylinders are designed to be field-repaired. Repair kits include two cable assemblies for double-acting cylinders (one for single-acting), with the main gland seal manufactured onto the cable, plus terminal ends and a seal kit covering all wearable seals. We also offer repair kits compatible with other manufacturers' cable cylinders.
Steps for cable replacement:
- Dismount the cylinder from the machinery.
- Disconnect cables from the clevis or load bracket.
- Remove sheaves from both cylinder heads. Retain the retaining rings.
- Remove the seal gland retaining ring from each head. Retain the retaining rings.
- Remove the tube retaining socket head cap screws from each head.
- Grasp one cable and pull the piston toward one end until exposed.
- Disconnect the cables from each end of the piston.
- Pull the cable assembly back through each head to remove.
- Thread a new cable assembly through the head in reverse order. Lubricate the O-rings on the cable gland O.D. Take care reseating the integral gland — do not use sharp instruments, which can damage the cable seal or nylon jacket.
- Inspect the cylinder tube I.D. Apply STP® 4-Cylinder Oil Treatment or equivalent if lubrication is needed.
- Reinstall the seal gland retaining ring.
- Replace all seals and gaskets.
- Reconnect the cable assemblies to the piston. Use Loctite® 242 (Blue) or Permabond #MM-115 on all piston terminal connections.
- Insert the piston back into the tube, gently tucking the piston U-cups into the tube using a blunt instrument.
- Reattach the cylinder heads using socket head cap screws, taking care to align the heads correctly.
- Remount the sheave assemblies.
- Reconnect the cable assemblies to the clevis or load bracket.
- Test for function and leaks.
- Reinstall the machinery and perform proof-loading and pre-tensioning before returning to service.
We recommend keeping a repair kit on hand for each cable cylinder model in your facility to minimize unplanned downtime.
Are repair kits available for non-W.C. Branham cable cylinders?
Yes. We offer aftermarket repair kits compatible with other manufacturers’ cable cylinders. Contact our customer service team with the make, model, and bore size for availability.
Ordering and Support
What configuration options are available?
Across the cable cylinder lineup, standard configuration options include:
- Auto tensioners — maintain cable tension in high-cycle and vertical lifting applications
- Reed switches — for position sensing (aluminum tubing models)
- Caliper disc brakes — for mid-stroke positioning and end-of-stroke deceleration (1.5" bore and larger; requires auto tensioner)
- Double stroke — doubles stroke and velocity within the same body length
- Single acting — one-directional actuation with gravity return
- Viton seals — for elevated temperature or chemical compatibility requirements
- Linear ball bearings — available on select guided cable cylinder models
Not all options are available on all models. Contact W.C. Branham or use the 3D product configurator at wcbranham.com to confirm available combinations for a specific bore size and type.
How do I get technical assistance or request sizing help?
We provide engineering support for cable cylinder selection and sizing. A sizing worksheet is available in the cable cylinder catalog — complete it with load weight, stroke, velocity, coefficient of friction, cycle rate, operating pressure, orientation, and environment details, then submit for a factory sizing recommendation.
- Phone (toll-free): 1-800-428-1974
- Phone (direct): 715-426-2000
- Fax: 715-426-1400
- Email: AskWCB@wcbranham.com
- Website: wcbranham.com