Pump and method for drawing vapor from a storage tank without forcibly drawing the vapor from the tank

A vapor transfer pump for a storage tank includes a bladder and a continuously reciprocating plate disposed about the bladder. Vapor from the storage tank enters the bladder through a one way check valve set at a low pressure, and is forced out, by the continuously reciprocating plate, through a second one way check valve set at a higher pressure.

FIELD OF THE INVENTION 
This invention relates to pumps, valves and the like for the transfer of 
vapour away from stored flammable materials and the like. 
BACKGROUND AND SUMMARY OF THE INVENTION 
When oil or other flammable materials are stored in liquid form, as for 
example in well head production tanks, vapour from the oil or from gases 
entrapped with the oil often escapes the oil and may be released into the 
atmosphere from the storage tank where it can be easily ignited or cause 
an environmental danger due to its toxicity. It is therefore desirable to 
pump the vapour away from the oil storage area and burn it in a controlled 
manner at a flare stack. 
The inventor has found that drawing vapour from the oil storage tank can 
create a dangerous condition by drawing air into the storage tank from the 
atmosphere. This occurs if, in pumping the vapour from the storage tank, a 
vacuum is created in the outlet line from the oil storage tank. 
The inventor has therefore provided a device that places constant pressure 
on the storage tank while allowing vapour to be pumped out of the storage 
tank. 
Therefore in one aspect of the invention, the inventor has provided a 
vapour transfer pump for a storage tank comprising: 
an inlet line connected to the storage tank; 
a first one way check valve on the inlet line; 
an expandable container connected to the inlet line; 
first means disposed about the expandable container and reciprocable 
independently of the expandable container for forcing vapour out of the 
expandable container; 
second means to reciprocate the first means about the expandable container; 
an outlet line connected to the expandable container and connectable to a 
flare stack; and 
a second one way check valve on the outlet line. 
In a preferred embodiment, the expandable container is a bladder, and the 
first means is formed from a stationary plate and a reciprocating plate, 
the bladder being disposed between the stationary plate and the 
reciprocating plate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 shows a production tank 10 with line 12 attached to it for venting 
gases or vapour from the tank. Typically at a production well head this 
tank will contain oil. Line 12 runs out to the vapour transfer pump 
generally designated 14 where it constitutes an inlet line for the vapour 
transfer pump. A first one way check valve 16 preferably of the flapper 
type which operates one way under minimal pressure is placed on the inlet 
line. 
The vapour transfer pump 14 is contained in a pump housing 20, which is 
preferably made of steel and is heated in conventional manner to provide 
protection to and warm operating conditions for the pump. The vapour 
transfer pump 14 includes an expandable container 22, preferably a rubber 
bladder (in the form of a torus), connected to the inlet line 12 through 
connection line 24. The expandable container 22 is disposed within a first 
means 26 which is reciprocable independently of the expandable container 
22 for forcing vapour out of the expandable container 22, under reciprocal 
movement created by a second means 34, including hydraulics, to be 
described in more detail below. 
An outlet line 44 is connected to the expandable container 22 through 
connection line 24. The outlet line 44 is connectable to a flare stack 
(not shown, but well known in the art). A second one way check valve 46 on 
the outlet line 44, also preferably a flapper valve, allows outflow of 
vapour to the flare stack but resists back flow of gas. A further high 
pressure check valve 48 is desirable on the outlet line to prevent over 
pressure conditions. Preferably this valve 48 should have a rating of at 
least 100 lbs. Methanol may be injected into the inlet line 12 at 50 to 
prevent freeze up. 
While the inlet line 12 and outlet line 44 have been shown entering and 
exiting the housing 20 at opposite sides, it is preferable that they enter 
and exit from the same side, adjacent each other, with the valves 16 and 
46 just inside the housing. In this way, the lines 12 and 44 can be easily 
detached from the valves 16 and 46, leaving the pump components as a unit 
that can be easily removed from the housing, for example on tracks, not 
shown, for maintenance. 
In the preferred embodiment, the first means 26 is formed from a stationary 
plate 30 and a reciprocating plate 32, the expandable container being 
disposed between the stationary plate 30 and the reciprocating plate 32. 
The reciprocating plate 32 is reciprocated by a second means 34 which 
consists of a shaft or piston rod 36, double acting hydraulic cylinder 38, 
connecting hoses 62 and 64, valve 40 with rod 54 and trip system including 
stops 56 and 58 (see FIGS. 2 and 3) on support 60 and hydraulic system 
with motor 70 (see FIG. 4). The motor drives a hydraulic pump 72 (see FIG. 
4) that supplies hydraulic fluid to the valve 40. Valve 40 directs the 
flow of hydraulic fluid to either side of the double acting hydraulic 
cylinder 38 through hoses 62 and 64, one on each end of the hydraulic 
cylinder. Double acting hydraulic cylinders are well known in the art so 
the operation of the cylinder to give reciprocal motion will be described 
here only briefly with reference to FIGS. 2 and 3. 
The shaft or piston rod 36 extends from the double acting hydraulic 
cylinder through a hole in the stationary plate 30, through the central 
part of the toroidal bladder 22 and attaches to the reciprocating plate 
32. The rod 54 extends up through both the reciprocating plate 32 and the 
stationary plate 30. The reciprocating plate 32 moves up and down as 
indicated by the arrows in FIG. 2 with the movement of the shaft 36. The 
first stop 56 (shown on the rod 54) is set near the upper limit of 
movement of the reciprocating plate 32. The second stop 58 is placed on 
the rod 54 at a point near the stationary plate 30 and corresponds to a 
suitably compressed point of the bladder 22. The run of the plate 32 
depends on the length of the hydraulic cylinder. The rod 54 is free moving 
within a sleeve 80 attached to the support 60, for example by bolting or 
welding. The support 60 itself is attached to the plate 30. At a central 
point on the rod 54 there is secured a cam 82 with upper and lower sloping 
surfaces. At the lower end of the rod 54 is a pair of nuts or stops 84 and 
86, one on each side of the upper plate 90 of a box 92. The lower end of 
the box 92 is secured to the control switch 94 on the valve 40. The valve 
40 is preferably a spool valve. Attached to the support 60 at a central 
point is a bar 100 having pivotally attached to its extremities a pair of 
swinging arms 102 and 104. At the respective extremities of each of the 
swinging arms 102 and 104 there is a roller 106. The swinging arms 102 and 
104 abut against compression springs 114 and 112 respectively, themselves 
secured in frame 116 having angle ends 118 against which the compression 
springs 112 and 114 abut. 
The manner of operation of the trip system is as follows. Assuming we start 
with the reciprocating plate 32 travelling downward under hydraulic 
pressure in the cylinder 38 (as shown as the position in FIG. 2), 
hydraulic fluid will be flowing into the cylinder in hose 64 and out 
through hose 62. When the reciprocating plate 32 reaches its downward 
limit, it comes up against the stop 58 and forces the rod 54 and cam 82 
downward so that the cam moves between the sprung rollers 106. This 
compresses the springs 112 and 114, which, as the rollers 106 roll down 
the lower edge of the cam 82, force the rod 54 downward until stop 84 hits 
plate 90 and thus switch 94, which signals the valve 40 to switch the 
direction of flow in the hoses. Hydraulic fluid then flows into the 
cylinder 38 in hose 62 and out through hose 64. This reverses the 
direction of movement of the shaft 36, hence of plate 32. Plate 32 then 
travels upward until it meets stop 56, which then moves upward with plate 
32 until the cam 82 clears the rollers 106. As the cam 82 clears the 
rollers 106, compressing the springs 114 and 112, the return force of the 
compressed springs forces the rod 54 quickly down the upward slope of the 
cam 82, such that the stop 86 is forced up against the plate 90, thus 
switching the switch 94 on the valve 40. This again reverses the direction 
of flow in the hoses 62 and 64, and thus the direction of movement of the 
shaft 36 and plate 32, which returns to the position shown in FIG. 2. Thus 
the valve 40 and hydraulic cylinder 38 automatically reverse the direction 
of the movement of the shaft 34 to reciprocate the first means 26 about 
the expandable container 22. 
The hydraulic system is shown in FIG. 4. Motor 70 is electrically powered 
in known fashion and drives hydraulic pump 72. Flow from the pump 72 
passes down hose 74 through speed control 76 and gauge 78 to valve 40. The 
spool valve 40 preferably incorporates a bypass valve set at 3 lbs 
pressure so that if the hydraulics build up such a pressure level, then 
the reciprocating plate 32 can be set to idle until the pressure level is 
reduced, thus avoiding dangerous over pressure conditions in the 
hydraulics in the second means and bladder. Hoses 62 and 64 feed the 
hydraulic cylinder 38. Return flow is through hoses 75 and 77, and passes 
through conventional filter 73 and reservoir 79. The motor itself may be 
for example an onsite electric motor or if the oil well has one, a pump 
jack. 
The manner of operation of the vapour transfer pump is as follows. Vapour 
from the storage tank over a minimal pressure, less than 1/2 ounce, passes 
through the inlet line 12 and check valve 16 under pressure from pressure 
in the production storage tank into the bladder 22. The bladder then 
continuously fills up with vapour, absent other pressures on it. The 
reciprocating plate 32 moves up and down continuously independently of the 
bladder 22 under power from the second means 34. On the up stroke of the 
reciprocating plate 32, the bladder 22 fills with vapour, and on the down 
stroke the vapour is forced out of the bladder 22 out through the outlet 
line 44, second check valve 46 and high pressure valve 48 to the flare 
stack. In this manner, the tank may be evacuated and vapour forced out to 
a flare stack without putting a vacuum on the tank. 
Alternative Embodiments 
A person skilled in the art could make immaterial modifications to the 
invention described and claimed in this patent without departing from the 
essence of the invention.