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Determination of water resistance by Shirley Hydrostatic Head Tester

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Determination of water resistance by Shirley Hydrostatic Head Tester

Introduction: 

The merit of a fabric intended for rainwear, wagon covers or tents is judged, amongst other properties, by its ability to keep water out; conversely, when intended for hose pipes or canvas buckets, to keep water in. In another direction, some fabrics must exhibit the ability to absorb water rapidly, toweling being an obvious example. So there is a relation between water and textile materials which is very necessary for their end use.

Objective:

  1. To measure the water resistance of the given fabric.

Theory:

Water resistance is the force or pressure of water which it applied on textile material to keep out though it and the determination of this required pressure or force is very important for particular use of a fabric. Shirley Hydrostatic Head tester is used to determine this pressure of water. In this instrument the specimen holder consists a double-chambered cell; the internal diameter of the inner chamber is 5 cm. Circular specimens are clamped between rubber gaskets over the orifice. Compressed air enters the outer chamber through a tube B and displaced the distilled water contained in the chamber through communicating passages into the inner chamber, thereby forcing water up against the specimen. The clamp is provided with a skirt which prevents air from leaking continuously across the test specimen from inner to outer chamber or to the atmosphere. The tube is connected to a manometer and the pressure of water against the fabric is, for all practical purposes, the pressure shown on the adjustable scale mounted on one arm of the manometer tube. The air supply for the test is drawn from a reservoir of about 3 l capacity which is itself fed through a flow control device from a source which may vary between 4 and 20 in/lb2. The flow control device is so designed that once it has been set to give the required rate of increase of pressure of 10 cm of water per minute, the rate of loading will be within the specified limits of  cm/min up to the limit of the instrument. The maximum head attainable is 150 cm of water.

Apparatus:

  1. Crease recovery tester
  2. Water
  3. Template
  4. Canvas fabric.

M/c specification:  

  1. Name : Shirley Hydrostatic Head tester
  2. Brand : NEGRETTI & ZAMBRA, made in England.
  3. Capacity : 0-150 cm.

Description of the Machine:

In this apparatus or instrument, the specimen holder consists of a double-chambered cell; the internal diameter of the inner chamber A is 5 cm. circular specimens are clamped between rubber gaskets over the orifice. Compressed air enters the outer chamber C through communicating passage into the inner chamber A, thereby forcing water up against the specimen. The clamp is provided with a skirt E, which prevents air from leaking continuously across the test specimen from C to A or to the atmosphere. Tube B is connected to a manometer D. the water pressure is shown on the adjustable scale mounted on one arm of manometer tube. The air supply for the test is drawn form a reservoir. The flow control device F increases pressure at a specified set rate in cm of water /minute. The maximum head is attainable 150cm of water.

Sample:

  1. Spherical canvas fabric.
  2. Size: 6 cm diameter.

Atmospheric condition:

  1. Wet condition: –   26 ° c. & Dry condition: – 30° c.
  2. Difference between wet and dry bulb = 30° c-26 ° c.  = 4° c
  3. So, relative humidity (RH) = 70 %

Procedure:

Circular specimens 6cm in diameter are cut from the fabric to be tested in such a way as to represent the material available as fully as possible.

They may be cut marked with a template and cut with scissors with as little handling of the material as possible. Then the test cell is rinsed thoroughly with distilled water and filled to approximately 0.2 cm of the top. A test specimen is laid over the orifice.  The clamp which is similarly dried is placed in position and screwed down.  A control lap is turned to position no.1 (bent). This means that the air supply manometer and test cell communicate. The control tap is then immediately turned to position No.2 (Read). This allows the air supply and the test cell to discharge to atmosphere while the manometer remains at the pressure at which breakdown of the test specimen occurred. The value to pressure is noted. The control tap is next turned to position No.3 (test) which allows the manometer to discharge to atmosphere. Then the test specimen is removed, a satisfactory mean may generally be obtained from tests on ten specimens.

Data:

Table: Pressures found from the test.

Serial Number   Pressure

(cm)

Average pressure
           1       28            30.8
           2       30
           3       34
           4       29
           5       33
           6       31
           7       28
           8       32
           9       29
         10       34

 

Result:

The water resistance of the sample fabric is 30.8 cm water pressure.

Remark:

According to the type of fabric the resistance of fabric varies between 0 -150 cm. The sample of the fabric is a canvas cloth and its water resistance is 30.8 cm. So it may say that the fabrics resistant to water are enough for its end uses.

Conclusion:

I would like to thank our respected teacher for the important instructions. I am also grateful to our lab assistants for their kind help. This experiment helps me to know about the weight of fabric per unit area that is very important for textile testing. I think this will be very helpful in my future life.

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