Proving Tanks are precision open volumetric calibrating measures. They enable on site calibration of liquid Flow Meters, Master Meters & vehicle tanks with high degree of accuracy & reliability.
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DESIGN FEATURES

• Rugged & fully welded construction.
• Displacement tube for accurate volumetric adjustment.
• Internal baffle plate prevents vortex formation & related trapping of air.
• Provision to fix thermometers & level bottle for accurate liquid measurement.
• Fixed or mobile versions with or without pump & motor.
• Top or bottom loading models.

PRINCIPLES OF OPERATION

Proving Tanks are manufactured as per standards laid down in IS:2341-1963 & Weights & Measures manual Vol. I Schedule V part XII 1974.

A Proving Tank consists of a cylindrical body welded between two conical ends which ensures smooth flow of liquid while draining the tank. Fitted to the bottom cone is a 'T' joint with inlet & outlet plug valves to assist in filling & draining of the tank. Also fitted to the draining tube attached to the 'T' is a drain valve & a sight glass to ensure complete draining of the tank.

The top cone is fitted with a neck tube having a conical top cover to prevent ingress of dirt in the tank. Externally fitted to the neck tube is a graduated glass tube which indicates the level of the liquid in the neck tube, the graduations corresponding to volume per unit height of the neck tube.

The cylindrical body has a manhole fitted with a bolted cover which can be opened for internal inspection, painting etc. A displacement tube arrangement is provided on the top cone to adjust the internal tank volume with the tank capacity mark on the graduated gauge glass tube. For accurate adjustment of tank level rest pads are fixed to the top cone for keeping level bottles. The body also has two thermo-wells capable of accepting mercury in steel thermometers.

A baffle plate provided at the point of liquid entry in the bottom cone prevents swirl, vortex formation & related trapping of air in the liquid. The entire tank is erected on a sturdy steel channel frame which can be either grouted for a Fixed Proving Tank or bolted to a movable trolley in case of a Mobile Proving Tank. In the latter case the trolley comes with a tow bar & leveling screw jacks. The choice of a centrifugal pump optional with a motor & a starter to fill or drain liquid optional both for fixed or mobile tanks.

PROVING TANK CALIBRATION

Before the calibration of the Proving Tank it has to be ensured that the bottom loading & unloading valves along with the drain valve are closed. The manhole cover is securely bolted & the displacement tube inserted to approximately half its length into the tank. With the help of level bottles the tank is correctly leveled. It is generally recommended to use a light petroleum distillate for tank calibration to minimise aeration of the liquid. Using verified measures liquid equal to the tank capacity is poured into the Proving Tank.

The level of the liquid in graduated the glass tube is noted. If the level of the liquid does not match the tank capacity mark on the graduated gauge glass the displacement tube is either inserted or retracted to exactly match the liquid level with the tank capacity mark on the graduated gauge glass tube. Tank calibration at this stage is complete. The displacement tube, manhole cover & the graduated gauge glass is then sealed. The average temperature of the liquid in the tank noted & is painted on the tank for further reference.

FLOW METER CALIBRATION USING FIXED PROVING TANKS

The field mounted Flow Meter or Master Meter to be calibrated is fixed in the pipeline carrying liquid into the Proving Tank. The Proving Tank is filled once or twice to purge all air, stabilise temperature & wet the internal surface. A quantity of liquid equivalent to the tank capacity is then passed through the Flow Meter into the tank. While doing this the average temperature of liquid in the tank & the temperature of the liquid flowing through the Flow Meter is noted.

Since liquids, essentially petroleum products, expand & contract with increase or decrease in temperature, a temperature correction is applied to the liquid volume received in the tank based on the temperature difference of the liquid in the tank & of liquid flowing into the Flow Meter.

Liquids are also compressible & hence a temperature correction is applied on the volume received in the Proving Tank, which is at atmospheric pressure & the pressure gauge reading at the Flow Meter inlet. The Proving Tank volume also slightly changes due to metal expansion or contraction particularly if the temperature of the liquid in the tank is different than the temperature at which it has been calibrated. After applying the various corrections the final corrected volume is compared with the Flow Meter reading & the Flow Meter error factor calculated.

FLOW METER CALIBRATION USING MOBILE PROVING TANKS

The Proving Tank is towed & positioned in the loading bay or in an appropriate position in order to release the Flow Meter throughput easily into the Proving Tank neck tube via a rubber hose. The tank is leveled correctly with the help of screw jacks provided. The bottom discharge valves along with the drain valve are closed. Procedure for proving the Flow Meter is now exactly the same as that for a fixed Proving Tank.

APPLICATIONS

• Calibration of field mounted liquid Flow Meters or Master Meters.
• Vehicle tank calibration.
• Calibration of bulk measures.