The Bell Automatic Weight Control

The Bell Automatic Weight Control is the simplest, safest, most economical device ever designed to maintain precise weight on the bit during drilling and coring operations at all depths and in every formation. So widely accepted is the Bell Automatic Weight Control as a standard piece of drilling equipment it is frequently written into contract specifications. Fully pneumatic, it meets the most rigid safety requirements.

Drillers like it. It's never in the way. Even though it is essentially fool-proof, it is designed to fail positively to protect drilling equipment from damage.

it can be installed on any rig in less than 2.5 hours and removed in 20 minutes.

Control Panel

To maintain proper weight on the bit, the driller need adjust only the weight control knob, using the rig weight indicator as a guide. Drum crawler speed is governed by the differential of weight on the drill bit.

A recored may be added to document hookload or weight on the bit.

How It Works

Pneumatic diaphragm A, mounted on the deadline, is the sensing element which signals the remainder of the system that in insufficient weight rests on the bit. Pneumatic impulses from diaphragm A are converted in control box B into pneumatic pressures which drive the drum crawler air motor C. As the drum crawler is impelled forward, cable D raises the brake lever, releasing the drawworks drum. Drawworks drum movement, in turn, rotates drum crawler governor roller E. An interaction then is created which continues until the proper weight has been restored to the bit, as sensed by deadline diaphragm A. When diaphragm A again senses that insufficient weight rests on the bit, the cycle is resumed.

Pneumatic Diaphragm

The pneumatic diaphragm used in the Bell Automatic Weight Control was designed and built by Bell to sense deadline stresses without the variances common to hydraulic sensing devices. The result is greater accuracy and more rapid response to changes in weight on the bit.

Advanced Drum Crawler

Recent improvements in drum crawler design make it possible to engage or disengage the crawler from the drum before and after trips or connections simply by activating a valve. The new unit requires the drilling of only four holes in the drawworks guard for permanent installation. Crawler works equally as well on drawworks of all makes and styles.

Questions & Answers

What happens in case of a leak in the pneumatic signal system?

Only a major leak would affect the operation of the weight control and in this case there would be no feed off.

Is it necessary to disconnect the control panel when making trips or connections?


How is weight set?

The control knob is adjusted for the desired weight, using rig weight indicator as a guide.

What maintenance is required by the crawler?

It should be lubricated as directed.

What is the variation in weight on the bit?

Approximately 1,000 pounds.

Will the unit hold constant weight when drilling with no more than 4,000-6,000 lbs. on the bit?

Yes. The drilling control will hold any given weight from 1,000 lbs. up.

What range of penetration rates will it control?

From zero to 180 feet per hour.

Why is the Bell Automatic Driller not connected directly to the weight indicator on the rig?

It can be, but experience has provied it to be more practical to use on independent pneumatic control system.

How can I obtain a Bell Automatic Driller?

The Bell Automatic Driller may be rented or purchased. Contact us for more information.

What happens if a twist-off occurs?

In case of twist-off, the action taken by the automatic driller depends on the weight of pipe twisted off and left on bottom. If the weight of the pipe on bottom is less than the weight for which the automatic driller is set, it will feed off until the difference is set down somewhere. If the weight of the pipe twisted off is greater than the weight set to run on the bit, there will be no feed off after the twist-off.

Example 1: The automatic controls are set to maintain 30,000 lbs. weight on the drill bit. Twist-off occurs, leaving 20,000 lbs. on bottom. Result: feed off until 10,000 lbs. is set down somewhere.

Example 2: Controls are set for 30,000 lbs. on the drill bit. Twist-off occurs, leaving 35,000 lbs. on bottom. Result: no feed off.

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© Control Drilling Service (1987) Ltd.
5921 - 87A Street, Edmonton, Alberta, T6E 5W6
Tel: (780) 465-6006, Fax: (780) 469-8872, Cell: (780) 951-4128 or (780) 719-2260