Simple Pharmanotes

   Elutriation Tank. Elutriation is a process for separating particles based on their size, shape and density, using a stream of gas or liquid flowing in a direction opposite to the direction of sedimentation. The apparatus consists of a vertical column with an inlet near the bottom for suspension, an outlet at the base for coarse particles and an overflow near the top for fluid and fine articles.  One column will give a single separation into two fractions. If more than one fraction is required a number of tubes of increasing area of cross section can be connected in series.  The velocity of the fluid decreases in succeeding tubes as the area of cross section increases, thus giving a number of fractions.  These fractions are separated and dried. Continuous process. Particles with low density which are not in the path of fluid current remain unaffected. Commonly Asked Questions. With a well labelled diagram describe construction and working of “Elutriation Tank”...

  Bag Filter. Principle: Particle Size and density of particles. In a bag filter, size separation of fines (or dust) from the milled powder is achieved in two steps.  In the first step, the milled powder is passed through a bag (made from cloth) by applying suction on the opposite side of the feed entry. This facilitates the separation.  In the next step, pressure is applied in order to shake the bags so that powder adhering to the bag falls off, which is collected from the conical base. Construction: It consists of a number of bags made of cotton or wool fabric.  These are suspended in a metal container.  A hopper is arranged at the bottom of the filter to receive the feed.  At the top of the metal container, a provision is made for vacuum fans and exhaust through a discharge manifold.  At the top of the vessel a bell-crank lever arrangement is made to change the action from filtering to shaking. Working: (a) Filtering period :  During this perio...

  Principle: A current of air combined with centrifugal force is used.  The finer particles are carried away by air and the coarser particles are thrown by centrifugal force, which fall at the bottom. Construction: It consists of a cylindrical vessel with a conical base.  A rotating plate is fitted on a shaft placed at the center of the vessel.  A set of fan blades are also fitted with the same shaft.  At the base of the vessel two outlets are provided: one for the finer particles and the other for coarse particles. Working: The disc and the fan are rotated by means of a motor.  The feed (powder) enters at the center of the vessel and falls off the rotating plate.  The rotating fan blades produce a draft (flow) of air in the direction as shown in the diagram.  The fine particles are picked up by the draft of air and carried into the space of the settling chamber, where the air velocity is sufficiently reduced so that the fine particles are dropped...

  Cyclone Separator. Principle: It uses centrifugal force to separate solids from fluids.  The separation process depends on particle size and particle density.  Construction: It is made up of a short vertical, cylindrical vessel with a conical base.  The upper part of the vessel is fitted with a tangential inlet.  The solid outlet is at the base.  Fluid outlet is provided at the center of the top portion, which extends inwardly into the separator.  Such an arrangement prevents the air short-circuiting directly from the inlet to the outlet of the fluid. Working: The solids to be separated are suspended in a stream of fluid (usually air or water).  Such feed is introduced tangentially at a very high velocity, so that rotary movement takes place within the vessel.  The centrifugal force throws the particles to the wall of the vessel.  As the speed of the fluid (air) diminishes, the particles fall to the base and are collected at the solid ...

  Principle: Agitation by Oscillation. Particles are made to pass through different sieves placed in nests which oscillate back and forth in motion. Construction: Consists of a metal frame on which sieves of different no. can be mounted. The sieves are arranged in a dissenting order of mesh size. The metal frame is fixed using screws and a capping on a vibrating frame. The vibrating frame is operated by an electrical motor whose speed can be controlled. The timer helps in maintaining time of the operation. Working: The powder to be screened is kept on the uppermost sieve and is capped and bolted. The machine's timer is set to the desired time (Usually 20 mins) and operated at desired speed. The vibrations cause oscillations resulting in passing of material from one sieve to another. After a given time the machine is stopped, the metal frame is loosed and screens are separated to collect the material. Advantages: Easy operation. Less power consumption. Economical. Disadvantages: Fin...

  Size separation can be done by various methods as follows, Agitation: Sieves may be agitated in a number of different ways. Oscillation (move back and forth)  The sieve is mounted in a frame that oscillates.  Advantages: Simple method Disadvantages: The material may roll on the surface of the sieve and fibrous materials tend to “ ball ”. Vibration: The mesh is vibrated at high speed, often by an electrical device.  Advantages: The rapid vibration is imparted to the particles on the sieve and the particles are less likely to “ blind ” the mesh. Gyration: Sieve is rubber mounted and is connected to an eccentric flywheel which gives gyrating movement which helps particles passing the sieve. Brushing: A brush can be used to move the particles on the surface of the sieve and to keep the meshes clear. A single brush across the diameter of an ordinary circular sieve, rotating about the midpoint, is effective; In large-scale production a horizontal cylindrical sieve is emp...

  Pharmaceutical Sieves. Sieves are the simplest and sieving is the most frequently used method for size separation. Construction: Sieves for pharmaceutical testing are constructed from wire cloth with square meshes, woven from wire ,of brass, bronze, 'stainless'' steel or any suitable materials . Sieves should not be coated or plated. There must be no reaction between the material of the sieve and the substance to be sieved .  Types of Sieves: Woven wire sieves . Plain weave Twilled weave Bolting cloth sieves . Bar screens . Punched   plates ( Perforated Screens ) Standards of Sieves: Common standards used for sieves are:  (a) Tyler standard sieve series (in USA)  (b) US standard. sieve series (in USA)  (c) British standard sieve series (in UK)  (d) German DIN (Deutsche lndustrienormein) (in Germany"and Europe)  (e) IP standard sieve series (in India)  (f) International test sieve series (ISO) (World wide). It is required that wir...