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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the passage of hydraulic pigging systems through
pipelines and other conduits. More particularly, it relates to a water
pumper facilitating the movement of pig devices through such lines.
2. Description of the Prior Art
Pigging systems are commonly employed in order to clean or condition the
inside surfaces of pipelines or other conduits. In normal pigging
operations, a high flow of a propelling fluid is required at moderate
pressure levels. During movement of the pig device through a line,
however, the resistance to travel occasionally increases. Such increased
resistance may be due to a variety of factors. During cleaning operations,
the most common cause is the encountering of the pig with a thicker
deposit on the wall of the line. This resistance to travel causes the pig
to slow down or even to stop in the line. The propelling pressure then
required to move the stuck pig forward, even at a slower rate, can be
several times higher than the normal pressure required to move the pig
before it became stuck in the line.
Centrifugal pumps commonly used to propel a pigging system through a line
are capable of delivering high water or other liquid flow at a moderate
pressure level, typically on the order of 300 psi. If higher pressures are
required when using the typical centrifugal pump approach, identical pumps
are commonly employed in series in order to achieve the desired higher
flow pressure. For example, two centrifugal pumps of 300 psi capacity
would be connected for series flow to get a 600 psi pressure level, three
such pumps would be piped in series to obtain a 900 psi pressure, and the
like. Higher flow rates would be accomplished with a larger impeller unit
or by adding additional pumps in parallel. Operating in this manner, the
pump system is sized for the maximum flow rate desired, and additional
stages are added in series to achieve the maximum pressure desired for a
particular operating circumstance.
Such practice of sizing a pumping system to deliver both the maximum
required flow and the maximum required pressure results in a larger, and
hence more expensive, pumping system than would be required for either the
maximum flow or the maximum pressure alone. The use of a larger pump also
requires the use of a more powerful driver and associated higher capital
and operating costs.
There is a genuine desire in the art, therefore, for improved pumpers for
the passage of pigging systems through lines. More particularly, it is
desired to enable pigging operations to be carried out using less
expensive pumping equipment capable of conveniently satisfying the unique
problems encountered in pigging operations.
It is an object of the invention to provide a water or other fluid pumper
suitable for use with hydraulic pigging systems.
It is another object of the invention to provide a water or other fluid
pumper system capable of advantageous use in propelling a pigging device
through a line and overcoming resistance to travel of said device.
With these and other object in mind, the invention is hereinafter described
in detail, the novel features of the invention being particularly pointed
out in the appended claims.
SUMMARY OF THE INVENTION
A pumper system is employed that enables pumps to run either in parallel or
in series in pigging operations. By enabling two pumps to run in parallel,
the requirements for high flow in pigging operations can be achieved. By
switching the same two pumps to series operation, the high pressure
required to move a pig device that becomes stalled in a line is achieved
at a moderate but acceptable flow rate.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is hereinafter described in detail with reference to the
accompanying drawings in which:
FIG. 1 is a schematic flow diagram of an embodiment of the pumper of the
invention; and
FIG. 2 is a schematic flow diagram of an alternative embodiment of the
invention adapted to provide additional flow pressure to overcome an
obstacle to the flow of a pig device in a line.
DETAILED DESCRIPTION OF THE INVENTION
The objects of the invention are accomplished employing a dual pump system
that is capable of operating in series or in parallel to meet the unique
requirements of pigging operations. By enabling switching of pumps between
high flow and high pressure conditions as needed, the pumper system of the
invention enables smaller, less expensive pumps to be advantageously
employed in pigging operations.
It should be noted that, in the field of fire fighting trucks, centrifugal
water pumps have been designed with two stages that can be operated in
parallel for extremely high flow at 300 psi, or in series for lower flow
at 600 psi. In addition, an optional third stage can be employed to boost
the pressure from the first two pumping stages to 800 psi, for long range
fire fighting requirements. The pump is designed with the outlets from the
third stage completely independent form the first two stages. Such a
pumper, with one outlet for high flow and a second one for high pressure,
while advantageous for fire fighting purposes, would be impractical for
efficient pigging operations.
In the practice of the invention, the supply of fluid for the third stage
is supplied by the discharge of the first two pump stages. A single
discharge pumper of the invention ties the discharge from the third stage
into the discharge of the first two stages downstream of the supply line
to the third stage, with a check valve being employed in between to
prevent recirculation through the third stage. This configuration is
uniquely different from that used on prior art hydraulic pigging pumpers
for fire truck applications. Thus, the pumper system of the invention can
be run with the supply valve to the third stage open, and the unit will
supply high flow rates at low pressure. If the pig becomes stuck, the
third stage will kick in to supply additional pressure. In such
embodiments, the invention automatically provides the pressure capability
that would normally require the use of a positive displacement pump, while
still providing the high flow capacities desired at lower pressures.
The invention involves modification of conventional pumper systems to
enable automatic switching from high flow rate, moderate pressure
operation to high pressure conditions when the need is encountered upon a
pig device becoming stuck in a line. In one embodiment of the invention, a
switchable parallel-series pump system is adapted for use in pigging
operations. The system has two, or more, identically sized pumps, which
are piped to allow operation of the pumps in parallel for normal pigging
operations. When a restriction is encountered in the line being treated,
the operation of the pumps is switched to series flow in order to provide
higher pressure, moderate flow conditions until the resistance to pig flow
is overcome.
In FIG. 1 of the drawing, feed inlet line 1 is connected to pump 2, the
discharge of which is passed, in line 3 to two-way valve 4, with the
suction of pump 2 likewise being passed in by-pass line 5, to said two-way
valve 4. Fluid from two-way valve 4 is passed in outlet line 6 to pump 7
from which fluid is discharged in outlet line 8 for passage to the
pipeline or other conduit being treated by the passage of a pig device
therefrom under the propelling force of the water or other fluid passing
from the illustrated two pump system. By-pass line 9 containing check
valve 10 extends from line 3 to outlet line 8.
In the operation of the FIG. 1 embodiment, two-way valve 4 switches the
suction of pump 7 from the discharge of pump 2 in line 3 to the suction of
pump 2 in line 5. This switches the two pumps from parallel operation to
series operation. In said parallel operation, pump 2 suction in by-pass
line 5 passes to pump 7, and pump 2 discharge passes in by-pass line 9 to
join pump 7 discharge in outlet line 8. In said series operation, the
discharge in line 3 from pump 2 passes to the suction of pump 7 in line 6.
In parallel flow operation, check valve 10 allows the discharge in by-pass
line 9 from pump 2 to flow to the discharge from pump 7 in outlet line 8.
In series flow operation, check valve 10 precludes the back-flow passage
of gas in by-pass line 9, while the discharge from pump 2 passes in line 3
to two-way valve 4 and to line 6 for series flow passage to pump 7.
For the pigging operations to which the invention is directed, the pumper
normally operates in the parallel mode. If a restriction is encountered by
a pig device in the line being treated, so that higher pressure operation
is required, two-way valve 4 is moved from its parallel mode position to
its series mode position so that a high pressure, lower flow rate
operation pertains, to facilitate the overcoming of the restriction to
flow in the line being treated. Check valve 10 precludes the back-flow of
fluid in by-pass line 9 from outlet line 8 to line 3. When the restriction
has been overcome, two-way valve 4 is switched back to its position for
parallel flow operation, and normal pigging operations are continued on a
high flow rate, moderate pressure basis.
If the two pumps in series are not capable of providing sufficient pressure
to overcome an obstacle to pig movement in a line, a boost pump left
engaged and piped, as shown in FIG. 2 of the drawings, will automatically
provide even high pressure at lower flow rates. In this embodiment, the
elements common to those as shown in FIG. 1 pertain and operate as
described above. Accordingly, the numerals designating said common
elements are the same in FIG. 2 as in FIG. 1. Outlet line 8 in the FIG. 2
embodiment is passed, however, to boost pump 11 from which discharge fluid
is passed in outlet line 12 for use as a propelling fluid to facilitate
passage of a pigging device through a pipeline or other conduit being
cleaned or otherwise treated. By-pass line 13, containing check valve 14,
extends from line 8, downstream of by-pass line 9, to outlet line 12,
i.e., from the suction to the discharge of boost pump 11.
When the required pressure of the pumper system does not provide sufficient
pressure to overcome an obstacle to the movement of a pig in a line, boost
pump 11 engaged and piped as shown in FIG. 2 will automatically provide
even high flow pressures at lower flow rates. When the necessary operating
pressure is below the maximum pressure of the two pumps, i.e, pumps 2 and
7, operating in series, check valve 14 in by-pass line 13 allows the flow
of fluid to by-pass boost pump 11. When the pressure required for
downstream pigging operations exceeds the capabilities of the two pumps,
check valve 14 will close, due to the downstream pressure in outlet line
12 being higher than the upstream pressure in line 8, so that all of the
fluid flow will be through boost pump 11 rather than through by-pass line
13. In this manner, the additional pressure required to overcome an
obstacle to pig flow can be conveniently provided, so that the desired
cleaning or conditioning of a line can be continued.
Those skilled in the art will appreciate that various changes and
modifications can be made in the details of the invention as herein
described without departing from the scope of the invention as recited in
the appended claims. While use of a two-way control valve as described
illustrated in the drawings, is a conventional item readily available for
commercial use, and is a preferred element for use in the practice of the
invention, the function served by this valve, i.e., two way control valve
4, can be accomplished by other readily available means. Thus, individual
valves could be piped together and operated to serve the same purpose of
controlling the flow of fluid to or around pump 7 for series or parallel
operation.
Such valves can be of any basic type commercially available in the field.
Said two-way control valve, or said individual valves, can be manually
operated, remotely activated, or automatically activated by a suitable
process computer/controller system.
It will be appreciated that the propelling fluid for the pigging purposes
of the invention is conveniently water, but that pigging operations using
other propelling fluids can also be employed using the pumper system of
the invention. Said two-way control valve, or said individual valves, can
be manually operated, remotely activated, or automatically actuated by a
suitable commercially available process computer/controller system. Those
skilled in the art will also appreciate the any suitable, commercially
available fluid pumper units, conveniently centrifugal pumps, can be used
in the practice of the invention. As indicated above, such pumps having an
operating pressure level of about 300 psi are particularly suitable for
the pigging purposes of the invention, although other capacity pumps can
also be employed depending on the pumping capacity required for a
particular pigging operation. Likewise, the fluid flow rate requirements
of the pumping units employed will also depend on the particular operating
conditions applicable to a given pigging operation, e.g., the size and
length of a line to be treated, the nature and configuration of the pig
being used, the condition of the line being cleaned or treated, and the
like. Pumping capacities of about 250 to 1250 gpm, typically about 500 to
1,000 gpm, are generally suitable for purposes of the invention, although
other capacity pumps may be suitable or desirable depending on the overall
operating conditions pertaining to a given pigging application.
The invention provides a genuine benefit in the art of in-situ pigging
applications. By enabling a pump system to be switched between parallel
and series operation to achieve desired high flow or high pressure
conditions as required in the course of a pigging operation, capital and
operating cost savings are achieved, thus enhancing the feasibility of
employing the highly desirable and advantageous in-situ pigging approach
to the cleaning or conditioning of the inner surface of pipelines and
other conduits.
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