11.2 MOTOR:

11.3 DESCRIPTION:

The Liquid Oxygen Pump is a single stage, single acting piston pump. It is used for filling oxygen into cylinders up to a pressure of 150 Kgs./cm2.

The pump is designed for assembly in air separation unit that works by pumping liquid oxygen and gasifying the same in Heat Exchangers for final filling as gas in cylinders. Control of liquid feed is not necessary, because the pump is designed in accordance with the plant size and the liquid produced is constantly pumped off.

The drive unit is similar to any reciprocating machine with the crank shaft, flywheel, connecting rod, cross head etc. as can be seen from the drawing supplied with the manual.

The Liquid Oxygen Pump consists of a stainless steel inside liner with liquid in-let and evaporated gas outlet port. There are no valves on theses ports, which are closed by the piston itself on the pressure stroke. The third outlet is the main discharge outlet with the two non-return ball valves. The two valves remain firmly closed during suction stroke due to high pressure in partly filled cylinders.

To ensure that these valves are fully closed, a positive pressure of about 40-60 kgs/cm2 must be maintained on it. When a fresh batch of cylinders is taken for filling open the manifold valve slowly or uses a spare batch of cylinders to ensure a positive pressure on these valves. Most mul functions of the pump are due to these valves not closing properly.

When the pump is operated liquid oxygen from the main condenser enters the outer jacket of the pump. Some of this liquid evaporates due to heat produced in pumping and the vapor is passed out through the upper port back into the upper column as gas. The main stream of liquid oxygen is taken into the pump cylinder and compressed out by piston in the pressure stroke. This high pressure liquid oxygen passes through two non-return valves into the heat exchangers and then to the cylinder filling rack.

If the molecular sieve is not working properly, some carbon dioxide and moisture will condense into the condenser and will travel to the L.O Pump inlet where a filter is provided. The solid CO2 may block the filter and the pump will not operate efficiently.

In such an event the L.O. Pump should be defrosted. This way, the solid carbon dioxide will be removed and the pump will now work satisfactorily unless there is a continuous carry over of CO2. Drain a little L.O in a double walled Dewar's flask and check against light. If the liquid is turbid, there are CO2 crystals in it. If it is clear the fault is elsewhere.

11.4 ERECTION:

During dispatch of the plant, the drive unit along with the inside pump is detached from cold box. The drive unit should be placed on its foundation. The bolts connecting the drive unit mounting flange to the cold box should be loosely tightened. This piston rod is to be rightly connected to the cross head. Now, the alignment should be such as the piston rod in the dead center of stuffing box. This can be checked by means of a feeler gauge, around the piston rod in stuffing box casing. This clearance should be same for any forward and backward position of piston. When this is centralized, the piston moves smoothly. The connecting bolts can be tightened without upsetting alignment and the drive unit is to be grouted.

11.5 LUBRICATION:

Before starting the crank close is to be filled with oil at two thirds (2/3) of oil level gauge through the breather in the back side. The oil specification are : Viscosity 6.5 , at +50 DegC, specific gravity 0.91 kgs/cm2 , flash point +175 DegC and solidification point max 5 DegC. The oil should be changed in 1000 hours.

Oil is sucked from crank case through filter by gear oil pump, which is directly driven by crank shaft. There is a pressure regulating valve in the pump. The pressurized oil enters a pressure chamber and enters oil holes drilled through crank shaft, big and bearing, connecting rod, cross head. An oil pressure gauge P-16 is provided which should normally be 0.5 to 1.0 kg/cm2.

The end bearing of crank shaft main bearing is lubricated by splash of oil by the crank shaft. To avoid any escape of lubricating oil along the piston rod, a rubber '0' ring is provided around the piston rod. This '0' ring is held in position by a cover plate at front side (Piston end side) of crank case.

In spite of this precaution, oil wetting of piston rod is to be checked often. Remove oil film if any by spraying carbon tetrachloride. Any escape of oil from drive unit to pump side should immediately be attended to. As a precaution before starting the pump, the piston rod should be cleaned with CTC.

11.6 OPERATION:

Open return oxygen gas vent valve V8A gradually, watching upper column P3 pressure. Open liquid oxygen inlet valve V8 gradually. The level in upper column will fall down initially and then wait till it again builds up.

Check for liquid - flow by opening valve.
Check free rotation of flywheel by hand. Clean L.O Pump piston with CTC. Open Nitrogen purge for stuffing box.
Start L.O pump motor, check for right direction of rotation. It should be anti - clockwise when viewed from flywheel side.
Oil Pressure P-16 should build up to 1.0 kgs/cm2. If not release air through pressure gauge valve P16.
Check for flow of oxygen in vent at manifold.

During normal run, check for any gland leaks of liquid oxygen in piston rod of stuffing box. If it leaks, tighten gland nut after warming with warm water. If it further leaks, stuffing box asbestos pickings are to be change.

11.7 CAUTION:

Always keep the L.O Pump parts of pump unit free from oil and grease. Refer chapter on safety.

11.8 MAINTENANCE:

11.9 FILTER:

Remove cold box cover plate on right side in L.O. Pump housing. Remove slag wool, the filter and cover can be removed by opening its outer nut. An insert made of sintered bronze is fixed inside. It can be cleaned by initial blowing with high pressure nitrogen then CTC washing and again blowing with nitrogen. While fixing back sure there are no gas leaks, by conducting a pressure test.

11.10 CYLINDER PISTON AND PISTON RINGS:

The inside liner can be remove along with piston rod and rings. Detach piston rod from cross head by opening cross head cap remove. Remove stuffing box cover nut, lantern ring and pickings. Remove non-return valve on pump end side and cap nut. Pull out inside liner with a small puller. The liner with piston rod will come out. Remove piston rod from liner and inspect piston rings. There are four sets of Teflon rings and one guide ring. If the rings are damaged, replace them. Clean all parts with CTC. Fix new Teflon asbestos rope of 3 mm O.D, around liner. Push piston rod with rings inside liner. They should not be cut by port holes in to-and-fro motion. Insert the assembly as it was removed connect piston rod to cross head. Check head and clearance of pump to be not less than 1 mm. Fix cap on pump end. Assemble stuffing box with new graphite impregnated asbestos packings.