A gauge "bob" or "bar" is usually made from brass and weighs approximately one and a half pounds. They are typically 6 inches long; however, they can be longer. Their function is to provide a weighted free end to the tape, allowing it to be lowered into a tank and to provide tension on the tape to keep it taught, while measurements are being made. The difference between an innage tape and an outage tape is that the zero point of an innage tape is at the tip of the bob, while the zero point of an outage tape is the inside top of the spring snap catch (see diagram comparing the two types of tapes). You can use an innage tape to take innage or outage gauges; however, you can only use an outage tape to take outage gauges. Never use an outage tape to take innage gauges. An innage tape bob is usually round in cross section, while an outage tape bob is usually square in cross section. Water Gauge Bar: an extra long innage bob, usually 12" or 18" long. It should be round in cross section and pointed. They are used when a water cut falls on the snap clip of the tape or if there is a lot of residue in the tank which needs a heavier bob to penetrate it.
Water Indicating Paste: a paste that is spread, thinly, onto the bob and tape. It changes color when it comes into contact with water, thus indicating the level of the free water interface. Gasoline Indicating Paste : in very light petroleum, the level of the liquid cannot be read on the tape because the petroleum evaporates while the tape is being raised from the liquid. To overcome this problem, gasoline paste is applied to the tape. When the paste comes into contact with the petroleum, it changes color or dissolves, indicating the petroleum level. Note: Chalk should not be used in place of gasoline indicating paste. 3.2.5 Gauging Procedure Manual tank gauging requires three consecutive readings to be within a range of 3mm or 1/ 8 inch. These readings should be averaged and recorded to the nearest 1mm or 1/8 inch. If two readings are identical, these shall be used and recorded to the nearest 1mm or 1/ 8 inch. Tapes should be inspected daily; or, prior to each use, for unacceptable wear, kinks, etc. The tape and bob assembly should be checked for accuracy when new, and at least once per year afterwards.
3.2.4 Gauging Equipment The principal piece of gauging equipment is the "gauge tape". There are two types: an innage tape and an outage tape. Both types of tape consist of a stainless-steel graduated tape in a stainless steel "reel and crank" housing with a wooden or plastic handle. The free end of the tape is fitted with a spring snap catch which is used to attach the gauge "bob" or "bar".
Outage tape
Innage tape
17
16
15
14
6
13
5
12
4
11
3
10
2
9
1
8
Innage bob Scale zero
7
1
6
2
5
Note: When a water gauge bar is used, readings on the tape will not be accurate, because of the additional length of bob.
3
4
4
3
Outage bob
5
2
6
1
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