• The orifices are of the readily replaceable type permitting coverage of the complete viscosity range with one cup and interchangeable orifices. The orifice may be readily replaced if damaged rather than requiring replacement of the entire cup.
  
• The Gardco/Fisher Cups are produced with removable orifices of the GARDCO “snap in, snap out” type. Cup and orifice production tolerance permits replacement or interchange of orifice sizes without loss of acceptable cup accuracy. (Except when certified)
  
• Conversion formulas and table relating efflux time in seconds, to the nearest tenth of a second, to viscosity in centistokes are furnished with each Gardco/Fisher viscosity cup.

1. Adjust the sample to measuring temperature, usually 25°C (77°F)
   
2. Select the cup that will provide readings which are well within the cup range.
   
3. Make sure that the cup is clean and place it in its support.
   
4. Make sure that the cup is level.
   
5. Place a finger under the cup orifice and fill the cup with bubble free test material. The cup is full when the meniscus disappears where the liquid joins the sidewall of the cup. If the cup is over-filled, scrape the excess into the cup well with a spatula or by passing the cover plate across the top of the cup. Note: that the finger can be removed from the orifice when the cover plate is in place.
   
6. Start a timer as the cover plate is removed from the cup.
   
7. Determine the temperature of the efflux stream. If there is a significant change during the test it should be repeated.
   
8. Stop the timer at the first break in the efflux stream, one or two inches below the orifice.
   
9. Record the cup type and number, measured temperature and efflux time. For best accuracy, average three or more readings.
   
10. Promptly clean the cup giving special care to the orifice.

Most materials change in viscosity as a function of temperature. Those normally measured by viscosity cups change in the range of 3% to 8% per degree Celsius change in temperature. Usually, the higher the viscosity the greater the change. For acceptable accuracy, it is necessary to measure temperature at the same time that viscosity cup readings are taken. When many determinations are to be made on similar products in the same viscosity range, it may be helpful to produce a graph for converting measured temperature and viscosity cup efflux time in seconds to seconds at a specified temperature, normally 25° Celsius.

There are three variables to consider: viscosity, efflux time seconds and temperature. All three can be shown on a graph with a family of curves as shown in the following example. Viscosity level is indicated by the diagonal lines, increasing from the lower left to the upper right. Such a graph can be prepared for a given material by taking readings with the Gardco/Fisher cup over a limited temperature range as shown in the example. Within this limited range the plots of the obtained data will normally result in a straight line such as the heavy diagonal line. Draw parallel lines to the line of experimental data, as shown, representing different viscosity levels. Enter on the graph the material represented and the Gardco/Fisher cup number designation.

Use the prepared graph by plotting on it measured temperature and efflux time in seconds. At "A" in the example these values are 26.0°C and 39.5 seconds. Read parallel to the diagonal lines to the intersection with the heavy vertical line which is 25.0°C, the target temperature. Then, reading horizontally to the left, it is found that the correct efflux time in seconds at 25°C is 41.5. Similarly, at "B" in the example, it is found that a reading taken at 23.5°C, when corrected to 25°C, changes from 40.5 to 37.5 seconds.

Compensating for temperature measured close to 25˚C must be done with caution. Even within the limited range of ±2.0°C the variation of viscosity with temperature may not be linear and any thinning materials used to adjust viscosity may also change the rate of this variation

The Gardco/Fisher viscosity cups are precision instruments. They are ruggedly constructed and with reasonable care will give many years of satisfactory service, requiring only thorough cleaning following each use. Particular care should be used in cleaning the orifice to avoid leaving deposits or scratches on internal surfaces.

Never strike the orifice directly when removing it from the cup. Place the dowel rod furnished with the cup against the orifice and strike the dowel with a heavy object such as a paper weight and catch the orifice Prior to inserting an orifice into the cup, insure that the exterior of the orifice and the receiving cone of the cup are clean.

It is good practice to retain one or more standard oils which can be used to periodically insure that the cup retains its initial calibration. Such oils are available from the Paul N. Gardner Company. Refer to the Specification Table (Fig. 1) for the oil recommended for use with each cup/orifice combination.

Gardco produced viscosity cups are calibrated with standard "G" Series oils. Centistoke viscosity value
of these oils is traceable to the National Institute of Standards and Technology and are available from
the Paul N. Gardner Company.

Shown in the graph is the viscosity cup designation and the standard oil used for its calibration. Normally, cup calibration is at 25 degrees Celsius, shown on the graph by bold lines intersecting with the curve in the circle. This graph is included with each Gardco/Fisher Standard cup sold by Gardco.

Viscosity of most liquids, including the standard oils, are dependent on temperature. Efflux time in seconds for the indicated cup-oil combination from twenty (20) to twenty seven (27) degrees Celsius is shown in the graph. The cup may be checked with this graph and the indicated oil with reasonable accuracy within these limits. For best accuracy, the temperature of the standard oil should be 25 degrees Celsius. The standard oil value in centistokes is printed on the standard oil bottle label. Conversion from viscosity in centistokes to efflux time in seconds is by formula or table that defines the cup characteristics. The cup applicable formula and table are furnished with each cup sold as an additional customer service by the Paul N. Gardner Company or by licensed distributors.

The Fisher series of viscosity cups as originally designed and produced, provided some advantages
over other existing dip viscosity cups. They accommodated a larger sample of the test material. The orifice was considerably longer than its diameter resulting in cup efflux time more closely proportional to viscosity. However, there were deficiencies in the design. The cup was difficult to clean. It was costly to produce and to calibrate. A damaged or enlarged orifice resulted in necessity for replacement of the entire cup.

The Gardco/Fisher viscosity cups retain the original internal cup dimensions and the same orifice length and diameter but with the following improvements: The weight of the new cup has been reduced to 44% of the weight of the original cup for easier temperature control when cup and material are not at the same temperature. The orifices are of the readily replaceable type permitting coverage of the complete viscosity range with one cup and interchangeable orifices. The orifice may be readily replaced if damaged rather than requiring replacement of the entire cup. The design of the lower portion of the cup eliminates hard to clean areas. The design directs the flow of all test material from the outside of the cup away from the efflux stream improving cup accuracy. Rod supports are designed and secured to the cup in a manner to prevent drainage to the inside of the cup and to provide easier cleaning. In addition to physical improvements, the cups are furnished with conversion formulas and a table which relates the nearest tenth of a second of total efflux time to viscosity in centistokes. This table is particularly useful in determining efflux time in seconds when viscosity in centistokes is known.

The Gardco/Fisher viscosity cups are calibrated at time of manufacture to within 2% of target efflux time. This calibration is with standard oils traceable to the National Institute of Standards and Technology. At an additional cost any cup/orifice combination is available with a CERTIFICATE OF CALIBRATION. The procedures and conditions of calibration on which the certificate is based qualify under ANSI/NCSL Z540-1 or MIL-STD-45662A, as applicable, & conforms to ISO 9000 when ordered with certification.

The Gardco/Fisher cups are produced to very close mechanical tolerance in elaborate jigs and fixtures. Such equipment not only insures that each cup is correctly produced but also that all cups are identical. All parts of the cup are of stainless steel except for the orifice and the name plate. The following table (FIG. 1) provides operating range specifications and the graphs with the included mathematical formulas define the flow characteristics for each numbered cup/ orifice combination.

The Fisher series of viscosity cups as originally designed and produced, provided some advantages
over other existing dip viscosity cups. They accommodated a larger sample of the test material. The orifice was considerably longer than its diameter resulting in cup efflux time more closely proportional to viscosity. However, there were deficiencies in the design. The cup was difficult to clean. It was costly to produce and to calibrate. A damaged or enlarged orifice resulted in necessity for replacement of the entire cup.

The Gardco/Fisher viscosity cups retain the original internal cup dimensions and the same orifice length and diameter but with the following improvements: The weight of the new cup has been reduced to 44% of the weight of the original cup for easier temperature control when cup and material are not at the same temperature. The orifices are of the readily replaceable type permitting coverage of the complete viscosity range with one cup and interchangeable orifices. The orifice may be readily replaced if damaged rather than requiring replacement of the entire cup. The design of the lower portion of the cup eliminates hard to clean areas. The design directs the flow of all test material from the outside of the cup away from the efflux stream improving cup accuracy. Rod supports are designed and secured to the cup in a manner to prevent drainage to the inside of the cup and to provide easier cleaning. In addition to physical improvements, the cups are furnished with conversion formulas and a table which relates the nearest tenth of a second of total efflux time to viscosity in centistokes. This table is particularly useful in determining efflux time in seconds when viscosity in centistokes is known.

The Gardco/Fisher viscosity cups are calibrated at time of manufacture to within 2% of target efflux time. This calibration is with standard oils traceable to the National Institute of Standards and Technology. At an additional cost any cup/orifice combination is available with a CERTIFICATE OF CALIBRATION. The procedures and conditions of calibration on which the certificate is based qualify under ANSI/NCSL Z540-1 or MIL-STD-45662A, as applicable, & conforms to ISO 9000 when ordered with certification.

The Gardco/Fisher cups are produced to very close mechanical tolerance in elaborate jigs and fixtures. Such equipment not only insures that each cup is correctly produced but also that all cups are identical. All parts of the cup are of stainless steel except for the orifice and the name plate. The following table (FIG. 1) provides operating range specifications and the graphs with the included mathematical formulas define the flow characteristics for each numbered cup/ orifice combination.