pulleys - Portable Winch · PDF filepoRtable WIncH co. dealeRs GuIde 4.4 poRtable WIncH co. 1 819 563-2193 1-888-388-7855 .. pulleys & block and tackles systems HoW to attacH a pulley

PORTABLE WINCH CO. | DEALER’S GUIDE

pulleys & block and tackles systems

PORTABLE WINCH CO. | +1 819 563-2193 | 1-888-388-7855 | www.portablewinch.com 4.1

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pulleys &

block and tackles systems




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Pulleys are used to guide the rope at the correct angle or to increase the pulling capacity through a pulley system.

pulleys and block and tackle systems

Pulleys have two main functions:

1A deviation pulley is HIGHLY recommended. This is a single pulley and it is used to change the traction angle (upwards or to the side) or to keep the rope off the ground. For example, a deviation pulley used on a steep slope allows the operator to keep the winch level. On level ground, a small angle reduces the friction of the system and premature wear of the rope.

When working with ropes, pulleys are extremely useful for creating a mechanical advantage, that is to say de-multiplying (reducing) the force required to move a mass. With the correct number of pulleys, it is possible to move loads two, three and even four times greater than the force applied. A set of pulleys is called a block and tackle system (or a hoist).

BLOCK AND TACKLE SYSTEMDEVIATION


PORTABLE WINCH CO. |+1 819 563-2193 | 1-888-388-7855 | www.portablewinch.com4.4


HoW to attacH a pulley

Generally speaking, each pulley is attached to a solid anchoring point using a carabiner and a sling respecting the relevant safety factor. The customer should be aware that, for each of its pulleys, a carabiner with an appropriate capacity and a sling is required. See the following pages on safety factors.

a note on caRabIneRsWe offer three types of self-locking carabiners, classified according to their breaking point:

FR: 50 kN (5,100 kg - 1,1240 lb) FR: 70 kN (7,140 kg - 15,737 lb)

pca-1276 pca-1702 pca-1701FR: 25 kN (2,550 kg - 5,620 lb)




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deVIatIon

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A deviation pulley is often extremely useful. This is a single pulley used to change the traction angle (upwards or to the side) or to keep the rope off the ground.

For example, in the photo below, the winch remains aligned with the pulley regardless of whether the log moves from the left or to the right when pulled. Additionally, it is used to lift the front of the log slightly, thus reducing friction with the ground, which is advantageous.

Figure 1




dIRectIonal FellInG

There are several situations where it is preferable to secure a tree and direct it during felling:

• Trees leaning to the wrong side

• Trees with an unbalanced top

• Hung-up trees

HERE IS HOW:

1) Install the winch in a safe-zone away from the fall line.

2) Install a self-locking pulley at the base of a tree in the fall direction.

3) Attach the end of the rope as high as possible to the tree being felled (Figure 2a). Remember that the distance (D) between the attachment point and the felling cut acts as a lever.

4) If the tree is leaning significantly, you can connect a pulley to the tree with a sling and attach the end of the rope to the self-locking pulley or to another tree. Thus you can double the force exerted (Figure 2b).

5) Here is the felling method:

a. Cut the directional notch in the normal fashion.

b. Start the winch and apply tension to the tree until the engine stalls. The self-locking pulley will maintain the tension while the felling is carried out.

c. Perform the felling cut normally and secure the tree with wedges.

6) Start the winch and tilt the tree by pulling on the rope.

with a PORTABLE WINCH winch

ImpoRtantTHESE INSTRUCTIONS ARE NOT A DIRECTIONAL FELLING COURSE BUT RATHER A TECHNIQUE FOR USING THE WINCH. IF YOU ARE NOT SKILLED IN FELLING, PLEASE CONTACT A PROFESSIONAL.




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dIRectIonal FellInGwith a PORTABLE WINCH winch

D

Figure 2a

D

Figure 2b




block and tackle systems

The use of pulleys offers a mechanical advantage by de-multiplying the force required to move a mass. In this section, you will discover how to double, triple, quadruple or quintuple the capacity of a system by using pulleys.

In order to gain a mechanical advantage, at least one pulley must be attached to the load. Let’s look at some simple cases of block and tackle systems for pulling an object. In figure 3, there is no mechanical advantage because there is no pulley attached and the force applied to the rope is equivalent to the winch capacity (e.g. 1,000 kg with the PCW5000).

How to create a mechanical advantage

pullInG WItH ZeRo mecHanIcal adVantaGe X 1

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Figure 3




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pullInG WItH a mecHanIcal adVantaGe X 2

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In figure 4, a pulley is attached to the load and the end of the rope is attached to the winch’s anchoring point. There are two rope lengths, each applying a pulling force of 1,000 kg. The mechanical advantage is x2. For example, a force of 1,000 kg applied by a PCW5000 will move a 2,000 kg load.

Figure 4




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Figure 5




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Figure 6a




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pullInG WItH a mecHanIcal adVantaGe X 4 (alteRnatIVe optIon)

Figure 6b




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Figure 7




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lIFtInG WItH no mecHanIcal adVantaGe X 1The same principles apply to lifting. However, an additional pulley (compared with pulling) is required to obtain a similar mechanical advantage. In the figure below, no pulley is attached to the load so there is no mechanical advantage. The pulleys act as deviation pulleys and the maximum load which can be moved will be equal to the winch's capacity, e.g. 250 kg with a PCH1000.

Figure 8




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lIFtInG WItH a mecHanIcal adVantaGe X 2

Figure 9




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Figure 10




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Figure 11




Equipment manufacturers often provide a rating called Minimum Breaking Strength (MBS), which is the force required to make the equipment fail. No piece of equipment should ever be subjected to forces near its MBS. It is imperative to divide the MBS by an appropriate Safety Factor according to the activity. The Working Load Limit is generally the Minimum Breaking Strength divided by the Safety Factor: WLL = MBS/SF.

For example, the lifting of objects requires a higher safety factor than when pulling of non-rollable objects on the ground. Additionally, lifting activities are often subject to standards, laws and regulations. It is essential to refer to the local regulations in force in your region.

saFety FactoRs

• Pulling: 2 - 3

• Lifting: 5 - 6

• Rope: 7 - 10

• If a life depends on it: 10

eXamples oF saFety FactoRs

When pulling, the safety factor is relatively low (2-3 times) because the risk of serious accidents is a lot lower.

However, when lifting, we recommend a higher safety factor of at least 5 for fixed equipment (e.g. pulleys and carabiners) and at least 7 for moving ropes which can be easily damaged. If the operation is life critical, the recommended safety factor is 10.

For example, using a block and tackle system offering twice the capacity of the PCH1000 and wishing to maintain a safety factor of 10:

• The maximum force of the PCH1000 is 250 kg

• The mechanical advantage of the block and tackle system is x2, which means that the maximum force applied is 2 x 250 kg = 500 kg

• The safety factor is 10, thus 10 x 500 kg = 5,000 kg

• The recommended carabiners the PCA-1702 which has a minimum breaking strength of 5,100 kg

Safety factors recommended by Portable Winch Co.




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saFety FactoRs Portable Winch carabiners have varying minimum breaking strength. When the force exerted is multiplied through a block and tackle system, the carabiners located on each end are subject to significant forces. A sufficient safety factor must be used so that the equipment operates safely.

Refer to the table below to find out the safety factor obtained with each of the carabiners based on the load displaced.

When the minimum breaking strength of a single carabiner is insufficient to achieve the safety factor required, two carabiners can be used with opposite and inverted openings to double the minimum breaking strength as illustrated in the photo below.

saFety FactoRs

load WeIGHt (kG) pca-1276 (25 kn) pca-1702 (50 kn) pca-1701 (70 kn)

250 10.2 20.4 28.6

500 5.1 10.2 14.3

750 3.4 6.8 9.5

1,000 2.6 5.1 7.1

2000 1.3 2.6 5.3

3000 NA 1.7 2.4

pulleys - Portable Winch · PDF filepoRtable WIncH co. dealeRs GuIde 4.4 poRtable WIncH co. 1 819 563-2193 1-888-388-7855 .. pulleys & block and tackles systems HoW to attacH a pulley

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