US3764894A

US3764894A - Static charge tester

Info

Publication number: US3764894A
Application number: US00207232A
Authority: US
Inventors: W Dukek; D Caldwell
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1971-12-13
Filing date: 1971-12-13
Publication date: 1973-10-09
Anticipated expiration: 1990-10-09

Abstract

An apparatus whereby the tendency of fuels to build static charges is measured. Also, filters used in fuel delivery systems may be tested to determine their potential for developing static charges which could lead to hazardous conditions during filling of tanks. A known volume of fuel is passed in a controlled manner through a filter and the streaming current is measured by an electrometer. A comparison is made with standard fuels and/or filters to establish a relative charging tendency and thereby to predict the static discharge hazard which may be incurred.

Description

United States Patent [1 1 Dukek et al.

[ Oct. 9, 1973 1 STATIC CHARGE TESTER [73 Assignee: Esso Research and Engineering Company, Linden, NJ

22 Filed: Dec. 13, 1971 21 Appl. No.: 207,232

[52] US. Cl. 324/32, 73/61.1

[51] Int. Cl G01r 5/28 [58] Field of Search 324/32, 33, 72; 210/85; 73/61.1 R, 61 R [56] References Cited UNITED STATES PATENTS 3,478,578 11/1969 Dukek 73/61.l R 3,405,722 10/1968 Carruthers 324/32 OTHER PUBLICATIONS J. A. Carruthers and K. J. Marsh Charge Relaxation in Hydrocarbon Liquids Journal of the Inst. of Petroleum 48(462) 6/62 pp. 169-179.

E. C. Giamia, Jr. Procedure for Making Triboelectric Measurements RCA Engineer Engineering and Research Note 17(1) June-July, 1971 pp. 102-103 Primary Examiner-Michael J. Lynch Att0rneyLeon Chasan et al.

[57] ABSTRACT An apparatus whereby the tendency of fuels to build static charges is measured. Also, filters used in fuel delivery systems may be tested to determine their potential for developing static charges which could lead to hazardous conditions during filling of tanks. A known volume of fuel is passed in a controlled manner through a filter and the streaming current is measured by an electrometer. A comparison is made with standard fuels and/or filters to establish a relative charging tendency and thereby to predict the static discharge hazard which may be incurred.

7 Claims, 1 Drawing Figure PAitNIEU 91W 3.764.894

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, Mame 1 STATIC CHARGE TESTER BACKGROUND OF THE INvENTIoN The invention disclosed herein pertains to the general field of detection of the tendency of fuels and fuel filters to develop static charges during filling operations. Particularly, a portable static charge tester has been developed which is intended for field use in measuring and detecting the presence of potentially hazardous situations.

Explosions have taken place in connection with the handling of gasoline and jet fuels. Although volatile hydrocarbons may form flammable mixtures with air, particularly during the filling or emptying of storage tanks, an explosion cannot occur without a source of ignition. Static electricity has often been blamed for the ignition of such flammable mixtures. Static electricity may be produced when a liquid moves past the surface of a solid or another liquid. Liquids become charged with static electricity when they are pumped through pipes or filters, agitated in tanks, or when they are sprayed into another liquid. It is believed that the mechanism which produces static electricity is the adsorption of ions of one polarity on the solid surface with ions of opposite polarity remaining in the liquid and moving downstream with it. The flow of ions from the liquid stream constitutes an electric current known as a streaming current and this current produces a difference in electrostatic potential. The over-all process involving the adsorption of ions of one polarity and the transport of ions of the other polarity is called charge separation."

Since the magnitude of streaming current depends on the concentration of ions in the liquid, it is possible for large differences to occur between fuels that are substantially the same with regard to their gross properties. Small amounts of impurities may result in high concentrations of ions and cause wide differences in streaming 1 current and static charge separation. In addition, it has been suspected that filters which are commonly used in filling lines may also have wide differences in their ability to produce large charge, separations which may lead to hazardous static discharges. A more extensive discussion of this problem can be found in U.S. Pat. No. 3,l4l',l l3 to Munday et al., assigned to the assignee of the present invention.

Heretofore no convenient method has been developed for detecting potentially hazardous situations which relate to the properties of the fuels and the filters through which they are passed. In order to provide such a method, the present invention was developed for use in making field measurements to detect potentially hazardous situations. Although in principle the invention may take many forms, it has been found convenient to adapt equipment available for field testing for the emulsion forming tendency of fuels such as described in U.S. Pat. No. 3,478,578 to Dukek et al., also assigned to the assignee of the present invention.

SUMMARY OF THE INvENTIoN A sample of fuel is placed in a syringe especially adapted for continuous discharge at a constant rate. The sample is discharged from the syringe through an electrically isolated filter element. The filter element is connected to an electrometer which measures the streaming current developed and which may be translated into the static charge. Such measurements correlate with the level of hazard involved since the higher the streaming current the greater the probability that a discharge could occur which could ignite a flammable mixture resulting in an explosion. I

The method of the present invention may be used for comparison of various fuels by selection of a single representative filter which is used for all the fuels to be tested and the static charge differences measured relating directly to the property of the fuels under test. Alternatively, different filters may be compared by using a single typical fuel. For this purpose, samples may be removed from filters in commercial service and compared with new filters of the same typ or, filters in use may be selectively sampled over a period of time to determine if the removal of impurities by the filter may be creating an increasing tendency towards static charge buildup. If such is the case, the filter should be'replaced before a hazardous condition occurs.

The test is simple to perform and a commercially available tester presently in use for measuring the emulsion forming tendency of fuels may be adapted for the static charge test. A field test may be performed which has heretofore been generally unavailable and which can contribute substantially to the safe handling of highly flammable liquids. i

DESCRIPTION OF THE DRAWING The single FIGURE shows a preferred embodiment of the present invention.

DESCRIPTION OF THE BREFERRED EMBODIMENT The drawing shows an adaptation of equipment already used for measuring the emulsion forming tendency of fuels to measure static charge buildup associmade by a standard electrometer connected thereto and also to ground. The'filter sample 14 is placed between two filter screens 12 and positioned within the body 20 of the filter holder 10 by means of a lower gasket l6 and an upper O-i'ing 18. The filter holder body 20 is secured to the remainder of the apparatus by threading it to the filter holder retainer 22, which is positioned at the end of the sample delivery apparatus. The sample leaving the filter holder 10 will enter a receptacle 26. The filter holder 10 through retainer 22 is connected to a valve 28 used to block the flow of sample until the test procedure is to begin. The valve 28 is connected to a non-conductive syringe 30 which receives a sample of the fuel to be tested. in order to avoid external influences the filter holder 10, valve 28- and grounded receptacle 26 are enclosed in a conventional Faraday cage 24. Contact between the valve and the cage must be avoided. The sample depicted to be within the syringe is designated 32. The sample is expelled from syringe 30 by means of a suitable plunger 34. A piston 36 affixed to one end of the plunger 34 is made to fit close to the walls of the syringe 3,0. It moves downwardly to expel sample 32 trapped within the syringe 30, forcing it through filter 14, thus creating a static charge buildup measured by electrometer 60. The piston 36 is connected by means of a stiffened flat member 38 to a key 39 located at the top of the member 38. The key 39 is mounted in a corresponding keyway 40 formed in the rack Rack 42 is secured on either side by guides 50 and moves both up and down when driven by a grounded motor 48 connected for driving the rack through pinion shaft 46. The pinions 44 engage the rack teeth and move the entire rack assembly 42 up or down in order to move the plunger 34. To limit the travel of rack 42, limit switches 52 are provided at both ends. These switches 52 cut off electrical power to the motor 48 when the extremity of travel in either direction has been reached. The entire drive assembly is mounted on a base plate 56. At the lower end of base plate 56 is a retainer 54 for mounting the syringe 30 in a fixed position by means of a key 55 and keyway 57.

In operation, the plunger 34 is removed from syringe 30 (assumed to be empty). The filter holder already has been assembled to the retainer 22 with a new sample of filter material 14 as previously described and the valve 28 is closed. A sample of fluid to be tested, for example, gasoline or jet fuel, is poured into the syringe 30 and allowed to remain for a short period in order for any charge buildup from the pouring operation to relax. The plunger 34 is then inserted into the top of the syringe 30 and the key 39 slid into its proper position in rack 42. The rack at this time will be at the top of its travel as shown in the FIGURE. With the plunger 34 in position, the valve 28 is opened and the Faraday cage 24 is installed as shown in the FIGURE. By activating the motor 48 which drives pinions 44, the rack 42 will be driven from its uppermost position to its lower position at a predetermined rate regulated by speed regulator 58. At the bottom of its travel, essentially all of the sample will have been expelled from syringe 30 and as the rack touches the lower switch 52 it will automatically shut off the power to motor 58, thereby stopping the test. It is important that the sample be expelled in a uniform manner in order to insure a constant velocity of the sample through the filter and to attain a reproducible reading on the electrometer 60.

During the period of travel of the plunger from its uppermost to lowermost position, a recorder (not shown) is attached to electrometer 60 which measures and gives a direct reading of the static charge buildup (the streaming current). In most cases, the streaming current attains a uniform value after an initial fluctuation associated with the start of flow. The electrometer 60 may be connected to a recorder if a permanent record is desired. Such measurements may be related as previously mentioned to the electrical properties of the filter itself or to the fuels which are being compared.

Although a commercially available motor-driven mechanism is illustrated herein, other means might be reservoir, in order to drive the plunger in a uniform manner. Accordingly, the invention should not be limited to the particular drive means, for example, a constant weight or fluid pressure might be used. Knowing the principle of operation of the invention, numerous other mechanisms might be devised to accomplish the same result. Only a currently preferred embodiment is illustrated herein and various modifications can be used without departing from the true spirit and scope of the invention as defined by the claims which follow.

What is claimed is:

l. A method of measuring the electrostatic charging tendency of a liquid comprising the steps of:

a. sampling a liquid to be tested,

b. introducing a fixed amount of said liquid sample into an electrically isolated sample holder,

c. allowing any charge developed during step (b) to relax,

d. transferring said liquid sample at a predetermined constant flow rate through an electrostatic charge generating means,

e. measuring the electrostatic charge buildup during passage of said portion through said electrostatic charge generating means.

2. The method of claim 1 further comprising the steps of:

a. repeating steps (a) through (e) of claim 1 using a second liquid sample to be tested,

b. comparing the electrostatic charge buildup from each of said samples and establishing the relative charging tendencies of each of said samples.

3. A method of measuring the electrostatic charging tendency of a filter comprising the steps of:

a. introducing a fixed amount of standard liquid into a reservoir,

b. allowing any charge developed during (a) to relax,

c. placing a filter sample into a filter holder electrically isolated from said reservoir,

d. transferring said portion of standard liquid through said filter holder at a predetermined constant flow rate,

e. measuring the electrostatic charge buildup on said filter holder during passage of said portion through said filter sample.

4. The method of claim 3 further comprising the steps of:

a. repeating steps (a) through (e) of claim 1 using a second filter sample,

b. comparing the electrostatic charge buildup from each of said filter samples and establishing the relative charging tendencies of each of said samples.

5. An apparatus for measuring the relative electrostatic charging tendency of liquids and filters compris- 5 ing in combination:

a. a tubular sample holder syringe, said sample holder having an internal portion adapted tto receive a sample of liquid to be tested and a plunger slidably mounted within said internal portion for expelling said sample of liquid from said internal portion,

b. filter holder means operatively connected to said sample holder syringe and electrically isolated therefrom, said filter holder adapted for mounting a filter sample,

0. drive means for operably moving said plunger at a constant rate thereby expelling at a constant flow rate a sample disposed in said sample holder syringe,

d. valve means operatively disposed between said sample holder Syringe and said filter holder means,

e. a sample receiver located adjacent said filter holder on the side opposite said valve whereby a sample expelled from said sample holder syringe and passing through said valve and said filter holder is accumulated in said sample receiver,

f. means connected between said filter holder and ground whereby electrostatic charge buildup on said filter holder relative to said ground is determined when a sample of liquid is expelled from said sample holder syringe through said valve and said filter holder into said sample receiver.

6. The apparatus of claim 5 wherein said means for operably moving said plunger comprises a pair of movable racks attached to said plunger and engaged by a pair of fixed coacting pinion gears, said gears being driven by anelectric motor.

7. The apparatus of claim 5 wherein the charge detection means of (f) is an electrometer connected between said filter holder and ground.

Claims

1. A method of measuring the electrostatic charging tendency of a liquid comprising the steps of: a. sampling a liquid to be tested, b. introducing a fixed amount of said liquid sample into an electrically isolated sample holder, c. allowing any charge developed during step (b) to relax, d. transferring said liquid sample at a predetermined constant flow rate through an electrostatic charge generating means, e. measuring the electrostatic charge buildup during passage of said portion through said electrostatic charge generating means.

2. The methoD of claim 1 further comprising the steps of: a. repeating steps (a) through (e) of claim 1 using a second liquid sample to be tested, b. comparing the electrostatic charge buildup from each of said samples and establishing the relative charging tendencies of each of said samples.

3. A method of measuring the electrostatic charging tendency of a filter comprising the steps of: a. introducing a fixed amount of standard liquid into a reservoir, b. allowing any charge developed during (a) to relax, c. placing a filter sample into a filter holder electrically isolated from said reservoir, d. transferring said portion of standard liquid through said filter holder at a predetermined constant flow rate, e. measuring the electrostatic charge buildup on said filter holder during passage of said portion through said filter sample.

4. The method of claim 3 further comprising the steps of: a. repeating steps (a) through (e) of claim 1 using a second filter sample, b. comparing the electrostatic charge buildup from each of said filter samples and establishing the relative charging tendencies of each of said samples.

5. An apparatus for measuring the relative electrostatic charging tendency of liquids and filters comprising in combination: a. a tubular sample holder syringe, said sample holder having an internal portion adapted to receive a sample of liquid to be tested and a plunger slidably mounted within said internal portion for expelling said sample of liquid from said internal portion, b. filter holder means operatively connected to said sample holder syringe and electrically isolated therefrom, said filter holder adapted for mounting a filter sample, c. drive means for operably moving said plunger at a constant rate thereby expelling at a constant flow rate a sample disposed in said sample holder syringe, d. valve means operatively disposed between said sample holder syringe and said filter holder means, e. a sample receiver located adjacent said filter holder on the side opposite said valve whereby a sample expelled from said sample holder syringe and passing through said valve and said filter holder is accumulated in said sample receiver, f. means connected between said filter holder and ground whereby electrostatic charge buildup on said filter holder relative to said ground is determined when a sample of liquid is expelled from said sample holder syringe through said valve and said filter holder into said sample receiver.

6. The apparatus of claim 5 wherein said means for operably moving said plunger comprises a pair of movable racks attached to said plunger and engaged by a pair of fixed coacting pinion gears, said gears being driven by an electric motor.