Manual of experiences ans tolerances in rope pump production


C.e. THE WHEEL.

TIRE RIMS AND THEIR DIAMETER.

The wheel is made from the two rims cut from tires with 20" hubcaps, usually used by buses and trucks. The rims are from the part of the tire that is mounted on the hubcap and always has steel wire in it for reinforcement. They are not the sides of the tires, which have been used in some previous rope pump designs. These tires always have wire in the part that is in contact with the road and in the rims used for rope pumps. Some brands also have this wire in the sides of the tires, making them inappropriate for the pumps as they are nearly impossible to cut and will always have wires protruding from the cut section.
Cutting these rims is an art. Experts in this activity need five minutes to cut two rims from a tire using a very sharp knife, a mallet and water for lubrication. Tire rubber is used for producing shoes, rocking chairs, beds, etc, causing tire rims to be known as waste from this industry. The cost of this material is minimal, less than a third of a dollar and with a little incentive the rims are cut correctly for use in rope pumps.

The rope touches the rubber on what was the inside part of the tire. This rubber often has an engraved design, which helps to avoid the rope sliding on the wheel. After a year or more of use, this design disappears leaving the surface smooth. After about three years of use the rubber becomes worn where the two rims meet and where the rope moves along it, exposing the wire threads.
The steel wires are located under this layer. As the rubber becomes worn with the movement of the rope, the surface becomes smoother and the rope tends to slide. This depends on the weight of the water column and the tension in the rope. Therefore, it is important to look at the functioning of the rope pump after several years of use.

The rims from these specific-sized tires are used for the following reasons:
  1. A large wheel implies more contact between the wheel and the rope than a smaller one (i.e. 16" hubcap) and therefore less sliding. The limits of 11, 19 and 29 meters are also based on sliding problems, which appear over time.
  2. Using rims from smaller tires implies that the force to be applied to the crank will be smaller and at the same time less water will be pumped. To compensate for this, the crank must be turned more rapidly, which is less comfortable.
  3. Rims with smaller diameters (20") have less consistency, are more flexible and require more clamps and support when used in a rope pump.
Using a tire for a 20" hubcap leads to an optimum use with regard to : This situation is coincidental and moreover, the 20" diameter is the size most commonly found on the market. A smaller wheel could result in a more esthetically pleasing image. The pumps are used on different ranges of depth and therefore it is impossible to speak of an optimum situation for each depth. What is true for a rim from a tire using a 20" hubcap is true for those from larger or smaller-sized hubcaps at different depths. The problems arise in the limits of the ranges. Smaller rims are used for deeper wells with the same size pumping pipe, while the problems of sliding indicate the need for an application at less depth.
There are also 22" hubcaps whose tire rims require even more force to be applied, therefore their use is less advisable with regard to force and more advisable when avoiding sliding. Another design aspect that plays a role is the speed of the rope. If the rope moves very rapidly, it carries large amounts of water, which splashes off the wheel. This occurs when the pumping pipe is small compared to the depth of the well.
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