11.1 TECHNICAL DATA:
|Type of Pump
Number of Cylinders
Discharge Pressure (Final Max.)
125/150 tr/ R.P.M.
150 TO 165 Kgs./cm2
183 Deg. C.
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.
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.
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
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
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
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.
Always keep the L.O Pump parts of pump unit free from oil and grease. Refer
chapter on safety.
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
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.