Automatic Lubrication During Cable Pulling
AUTOMATIC LUBRICATION DURING CABLE PULLING
The Problem
The savings and benefits of automatically applying lubricant during cable pulling depend on installation specifics. A contractor pulling a few hundred feet of building wire into small conduit will have quite different needs from a utility crew pulling several thousand feet of underground distribution cable daily. Yet in both cases, some level of automation in the lubrication operation may be cost justified.
Automated lubrication can:
- Save time and manpower, usually by eliminating the need to dedicate a person to applying lubricant by hand.
- Save optimal lubricant quantity, that is, not using too much or too little lubricant.
- Provide thorough and consistent lubrication for lowest cable pulling tension.
How Much
We first need to know how much lubricant to use when pulling a cable. The equation below will tell us.
Q = K x L x D
Where
Q = Quantity of lubricant in gals (liters)
L = Length of conduit in feet (meters)
D = ID of the conduit in inches (mm)
K = Constant of 1.5 x 10-3 (English) or 7.3 x 10 -4 (metric)
This equation determines the amount of lubricant needed to completely coat the interior wall of a conduit with a lubricant film of 0.009 inches (0.2mm) thickness. The equation calculates lubricant quantities consistent with those used by experienced cable pulling crews.
How Much/How Fast
If we're going to pump the lubricant to the conduit entrance, we'll need the previous equation converted to a lubrication rate calculation:
R = K x D x S
Where
R = Lubrication rate in gals/min (liters/min)
S = Pulling speed in feet/min (meters/min)
At typical pulling speeds of 10 to 60 ft/min (3 to 18 m/min) and duct sizes of 2 to 6 inches (50 to 150 mm), the rate calculation provides expected lubricant demand from a low of 0.03 gal/min to a high of 0.5 gal/min (0.1 to 1.9 l/min). These are low volume flow rates that can be produced by a number of low-power pumps.
But first, what about smaller and/or less frequent pulls, where automatic pumping is not practical. Is there any better way to apply pulling lubricant than dipping into the lube bucket and applying it by hand?
Pump Selection
When choosing pumping systems for applying pulling lubricant, a pump should be selected that can handle both liquid and gel lubes at the needed flow rates. It is a mistake to compromise lubricant quality based on limitations in a pump's capability. The most important characteristics of pulling lubricant are that it is fully compatible with cable jackets and that it produces low friction in a broad range of field conditions, regardless of how it is applied.
A pump should not shear the lube or build pressure in the outlet hose when flow is reduced with a restriction valve. Pressure pots low-ratio piston pumps and air-operated diaphragm pumps all meet these criteria.
High shear pumps that run at a high constant speed (rotary vane, gear) are usually not appropriate for field lubrication. The continuous shear from the blades causes deterioration in lubricant performance and builds high pressure in the feed lines.
The diameter and length of the outlet hose on a pump are also important. The hose and any other line restrictions should be large enough to support the desired flow rates.
The usual question is whether a pump has enough draw to pull the liquid into the pump. One of the pump types we recommend, a "pressure pot", has all the liquid "within" the pump, so priming, draw, and cavitation are not concerns.
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"A CRASH COURSE IN SOLVING POWER PROBLEMS"
In recent years, the electronics industry has developed a variety of power protection devices to shield data and equipment from power-related damage. These devices fall into five distinct categories, each having different capabilities and limitations offering a different level of protection. Below is an explanation of these technologies and their effectiveness against specific power problems.
Surge suppressors or surge protectors are passive electronic devices that protect against transient high-level voltages.
Depending on the components involved, surge suppressors offer limited protection against power surges. In the case of high-voltage spikes, a high quality surge suppressor can be a good choice. When large equipment like AC motors are turned on and off, they create large, fast voltage changes (switching transients). However, low frequency surges (slow changes at 400 Hz or less) can be too great for a surge suppressor attempting to clamp that surge.
The simplest type of power protection device, surge suppressors are often used to shield important, but not critical or highly sensitive office equipment, such as copiers and fax machines, and may be a complement to more comprehensive power protection solutions.
Power line conditioners were one of the first power protection devices to come on the market. They were originally designed to shield small computer installations before the introduction of low-cost, small capacity surge suppressors and uninterruptible power systems (UPS's). These devices offer regulation over a certain bandwidth of voltage fluctuations.
Against power surges, high-voltage spikes and switching transients, power line conditioners provide a level of protection similar to that offered by surge suppressors. In addition, some protect against power sags and brownouts for up to two cycles, and are also an adequate solution for electrical noise problems.
The remaining power protection technologies are classified under the umbrella term Uninterruptible Power Systems (UPS's). There are three types of UPS's: off-line or standby; line-interactive or hybrid, and on-/ire.
Off-line or Standby UPS's consist of a basic battery/power conversion circuit and a switch that senses irregularities in the electric utility. The computer is usually connected directly to the utility that serves as the primary power source, and power protection is available only when line voltage dips to the point of creating an outage. Some off-line UPS's do include surge suppression circuits, and some possess optional built-in power line conditioners to increase the level of protection they offer.
In the case of power surges, an off-line UPS passes the surge voltage to the protected system until it hits a predetermined level, around 115% of the input voltage. At the surge limit the unit then goes to battery. With high-voltage spikes and switching transients, them give reasonably good coverage, but not the total isolation needed for complete input protection. For power sags, electrical line noise and brownouts, off-line UPS's protect only when the battery is delivering power to the protected system.
Line-interactive UPS's are hybrid devices that attempt to offer a higher level of performance by adding voltage regulation features to conventional off-line designs.
Like off-line models, line-interactive UPS's protect against power surges by passing the surge voltage to the computer until it hits a predetermined voltage, at which point the unit goes to battery. They provide moderate protection against high-voltage spikes and switching transients, although, again, not with complete isolation.
On-line UPS's provide the highest level of power protection and are the ideal choice for shielding your organization's most important computing installations. This technology uses the combination of a double-conversion (AC to DC/DC to AC) power circuit and an inverter, which continuously powers the load, to provide both conditioned electrical power and outage protection. On-line UPS's offer complete protection and isolation from all types of power problems - power surges, high-voltage spikes, switching transients, power sags, electrical line noise, frequency variation, brownouts and blackouts. In addition, they provide digital-quality power not possible with off-line systems. For these reasons, they typically are used for mission-critical applications that demand high productivity and systems availability.
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