Patent Publication Number: US-2022234881-A1

Title: Fuel delivery system and method

Description:
BACKGROUND 
     Technical Field 
     Fuel delivery systems and methods. 
     Description of the Related Art 
     Equipment at a well being fractured requires large amounts of fuel. Conventionally, if the equipment needs to be at the well site during a very large fracturing job, the fuel tanks of the equipment may need to be filled up several times, and this is done by the well-known method of manually discharging fluid from a fuel source into each fuel tank one after the other. If one of the fuel tanks runs out of fuel during the fracturing job, the fracturing job may need to be repeated, or possibly the well may be damaged. The larger the fracturing job, the more likely equipment is to run out of fuel. Dangers to the existing way of proceeding include: extreme operating temperatures and pressures, extreme noise levels, and fire hazard from fuel and fuel vapors. 
     BRIEF SUMMARY 
     A fuel delivery system and method is presented for reducing the likelihood that a fuel tank of equipment at a well site during fracturing of a well will run out of fuel. There is therefore provided a fuel delivery system for delivery of fuel to fuel tanks of equipment at a well site during fracturing of a well, the fuel delivery system comprising a fuel source having plural fuel outlets, a hose on each fuel outlet of the plural fuel outlets, each hose being connected to a fuel cap on a respective one of the fuel tanks for delivery of fuel to the fuel tank; and a valve arrangement at each fuel outlet controlling fluid flow through the hose at the respective fuel outlet. The valve arrangement may be a single valve, for example manually controlled. The fuel source may comprise one or more manifolds with associated pumps and fuel line or lines. Hoses from the manifolds may be secured to the fuel tanks by a cap with ports, which may include a port for fuel delivery, a port for a fluid level sensor and a port for release of air from the fuel tank during fuel delivery. The fluid level sensor combined with an automatically operated valve as part of the valve arrangement on the fuel outlets from the fuel source may be used for automatic control of fuel delivery. A manual override is preferably also provided to control fuel flow from the fuel outlets. 
     A method is also provided for fuel delivery to fuel tanks of equipment at a well site by pumping fuel from a fuel source through hoses in parallel to each of the fuel tanks; and controlling fluid flow through each hose independently of flow in other hoses. 
     A cap or fill head for a fuel tank is disclosed, comprising: a housing having a throat and a top end; a first port in the top end provided with a connection for securing a hose to the cap; and a second port in the top end holding a fuel level sensor. 
     These and other aspects of the device and method are set out in the claims, which are incorporated here by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which: 
         FIG. 1  is a schematic of a fuel delivery system; 
         FIG. 2  is a side view of a tank to which fuel is to be delivered; 
         FIG. 3  is a top view of a cap for delivering fuel to the tank of  FIG. 2 ; 
         FIG. 4  is a bottom plan view of a top end of a cap for delivering fuel to the tank of  FIG. 2 ; and 
         FIG. 5  is an exploded side elevation view, in section, of a fuel cap comprising the top end of  FIG. 4  assembled with an intermediate portion, a bottom end, and an overfill protection valve. A fuel tank fill riser and overfill protection valve are also included in the image. 
     
    
    
     DETAILED DESCRIPTION 
     Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims. In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite article “a” before a claim feature does not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims. 
     Equipment at a well site use for a fracturing job may comprise several pumpers and blenders. A representative pumper  10  is shown in  FIG. 1  with a fuel tank  12 . Typically, the fuel tank  12  comprises a connected pair of tanks. A fuel delivery system  14  is provided for delivery of fuel to multiple fuel tanks  12  of multiple pieces of equipment  10  at a well site during fracturing of a well. The fuel delivery system  14  may be contained on a single trailer, for example wheeled or skidded, or parts may be carried on several trailers or skids. For use at different well sites, the fuel delivery system should be portable and transportable to various well sites. 
     The fuel delivery system  14  includes a fuel source  16 . The fuel source  16  may be formed in part by one or more tanks  18 ,  20  that are used to store fuel. The tanks  18 ,  20  may be mounted on the same trailer as the rest of the fuel delivery system  14  or on other trailers. The tanks  18 ,  20  should be provided with anti-siphon protection. The fuel source  16  has plural fuel outlets  22 . Respective hoses  24  are connected individually to each fuel outlet  22 . Each hose  24  is connected to a fuel cap or fill head  26  on a respective one of the fuel tanks  12  for delivery of fuel to the fuel tank  12  through the hose  24 . Hoses  24  may each have a sight glass (Visi-Flo™, not shown) to check flow and observe air-to-fuel transition. Sight glasses may be used on hoses  24  or elsewhere in the system. Pressure meters (not shown) may be provided for example on each of the hoses  24  from the manifold to determine head pressure as well as deadhead pressure from the pumps  32 ,  34 . A valve arrangement, comprising for example valve  28  and/or valve  58 , is provided at each fuel outlet  22  to control fluid flow through the hose  24  connected to each respective fuel outlet  22  to permit independent operation of each hose  24 . The valve arrangement preferably comprises at least a manually controlled valve  28 , such as a ball valve, and may comprise only a single valve on each outlet  22  in some embodiments. The hoses  24  are preferably stored on reels  30 . The reels  30  may be manual reels, or may be spring loaded. In order to accommodate the weight of hoses  24  on reels  30 , the skid or trailer frame may have to be braced (not shown) sufficiently in order to prevent the hose  24  from forcing the frame open. Hose covers, such as aluminum covers (not shown), may be provided for capping hoses  24  that are not connected to fuel tanks  12 , as a precaution in the event of a leak from a hose  24  or to prevent leakage in the event fuel is mistakenly sent through a hose  24  not connected to a respective fuel tank  12 . 
     In the embodiment shown in  FIG. 1 , each tank  18 ,  20  is connected to respective pumps  32 ,  34  and then to respective manifolds  36 ,  38  via lines  40 ,  42 . The fuel outlets  22  are located on the manifolds  36 ,  38  and fluid flow through the fuel outlets  22  is controlled preferably at least by the manual valves  28 . In a further embodiment, the fuel outlets  22  may each be supplied fuel through a corresponding pump, one pump for each outlet  22 , and there may be one or more tanks, even one or more tanks for each outlet  22 . However, using a manifold  36 ,  38  makes for a simpler system. The manually controlled valves  28  are preferably located on and formed as part of the manifolds  36 ,  38 . 
     The fuel caps  26  are shown in  FIGS. 2 and 3  in more detail. Each fuel cap  26  is provided with a coupling for securing the fuel cap  26  on a tank  12 , and this coupler usually comprises a threaded coupling. The fuel cap  26  comprises a housing  43  with a throat  44 , threaded in the usual case for threading onto the fuel tank  12 , and top end  46 . Throat  44  may define a central housing axis  45  ( FIG. 3 ). A quick coupler, not shown, may be included between the top end and throat. The throat may be sized for different sizes of fuel tank inlets. In one embodiment, the fuel cap  26  comprises at least three ports  48 ,  49  and  50  in the top end  46 . One of the ports  48  may be provided as a breather port with a line  52  extending from the cap  26  preferably downward to allow release of air and vapor while the tank  12  is being filled with fuel. A pail (not shown) may be provided at the end of line  52  in order to catch any overfill. A one-way valve may be added to the breather port, for example to reduce the chance of fuel being spilled through the breather port during filling of fuel tanks  12  on equipment such as pumpers that vibrate violently. However, in another embodiment such fuel tanks  12  on violently vibrating equipment may simply be restricted from filling past a level relatively lower from non-vibrating equipment in order to reduce spilling. The cap  26  preferably seals the inlet on the fuel tank  12  except for the vapor relief line  52 . Each cap  26  also preferably comprises a fuel level sensor  54  mounted in port  49 . The fuel level sensor  54  may be any suitable sensor such as a float sensor, vibrating level switch or pressure transducer. A suitable float sensor is an Accutech FL10™ Wireless Float Level Field Unit. 
     The sensor  54  preferably communicates with a control station  56  on the trailer  14  via a wireless communication channel, though a wired channel may also be used. For this purpose, the fuel level sensor  54  preferably includes a wireless transceiver  55 , such as an Accutech™ Multi-Input Field Unit or other suitable communication device. Transceiver  55  may be provided with a mounting bracket (not shown) or clip for attachment to fuel tank  12 . This may be advantageous in the event that fuel tank  12  does not have sufficient headspace to allow transceiver  55  to be positioned as shown in  FIG. 2 . The control station  56  comprises a transceiver that is compatible with the transceiver at the sensor  54 , such as an Accutech™ base radio, and a variety of control and display equipment according to the specific embodiment used. In an embodiment with automatically operating valves  58 , the control station  56  may comprise a conventional computer, input device (keyboard) and display or displays. In a manual embodiment, the operator may be provided with a valve control console with individual toggles for remote operation of the valves  58 , and the valve control console, or another console, may include visual representations or displays showing the fuel level in each of the tanks  12 . Any visual representation or display may be used that shows at least a high level condition (tank full) and a low level condition (tank empty or nearly empty) and preferably also shows actual fuel level. The console or computer display may also show the fuel level in the tanks  18 ,  20  or the rate of fuel consumption in the tanks  18 ,  20 . 
     The port  50  may be used to house a conduit  27  such as a drop tube, pipe, or flexible hose that extends down through the cap  26  to the bottom of the fuel tank  12 , and which is connected via a connection  62 , for example a dry connection, to one of the hoses  24 . The conduit  27  should extend nearly to the bottom of the fuel tank  12  to allow for bottom to top filling, which tends to reduce splashing or mist generation. The conduit  27  may be provided in a length sufficient to eliminate generation of static electricity. A telescoping stinger could be used for the conduit  27 . If the fuel tank  12  has an extra opening, for example as a vent, this vent may also be used for venting during filling instead of or in addition to the port  48 , with the vent line  52  installed in this opening directing vapor to the ground. Where only the extra opening on the fuel tank  12  is used, the cap  26  need only have two ports. In another embodiment requiring only two ports, venting may be provided on the cap  26  by slots on the side of the cap  26 , and with the other ports used for fuel delivery and level sensing. To provide the slots, the top end of a conventional cap with slots may have its top removed and replaced with the top end  46  of the cap  26 , with or without the additional vent  48 , depending on requirements. A pressure relief nozzle may be provided on hoses  24 , or at any suitable part of the system in order to reduce the chance of pressure release upon disconnect or connection. A drain cock (not shown) may also be used to ensure that all pipes/hoses can be drained before removal. Each manifold may have a low-level drain. 
     The fuel delivery system  14  may be provided with automatic fuel delivery by providing the valve arrangement on the outlets  22  with an electrically operable valve  58  on each fuel outlet  22  shown in  FIG. 1  with a symbol indicating that the valve  58  is operable via a solenoid S, but various configurations of automatic valve may be used. The control station or controller  56  in this embodiment is responsive to signals supplied from each fuel level sensor  54  through respective communication channels, wired or wireless, but preferably wireless, to provide control signals to the respective automatically operable valves  58 . Each valve  58  includes a suitable receiver or transceiver for communicating with the control station  56 . The controller  56  is responsive to a low fuel level signal from each fuel tank  12  to start fuel flow to the fuel tank  12  independently of flow to other fuel tanks  12  and to a high level signal from each fuel tank  12  to stop fuel flow to the fuel tank  12  independently of flow to other fuel tanks  12 . That is, commencement of fuel delivery is initiated when fuel in a fuel tank is too low and stopped when the tank is full. A manual valve may also be provided for this purpose. Redundant systems may be required to show fuel level, as for example having more than one fuel sensor operating simultaneously. Having a manual override may be important to a customer. Manual override may be provided by using valves  28 , and may also be provided on an electrically operated valve  58 . The manual override should be provided on the low fuel side to allow manual commencement of fuel delivery and high fuel side to allow manual shut-off of fuel delivery. 
     Pump  32 ,  34  operation may be made automatic by automatically turning the pump(s) off after pressure in the system has risen to a predetermined level. For example, this may be done by adding a pressure switch (not shown) to the system, for example to the pump, which pressure switch would stop the power to the pump when all the valves, such as valves  28 ,  58 , are closed and the pump has built up pressure to a predetermined level. As soon as one of the valves is opened the pressure from the pump line would drop off and the pressure switch would allow power back to the pump unit, allowing the pump to start and push fuel through the lines. Once all valves are shut again the pump would build pressure up to the predetermined pressure and the pressure switch would sense the rise in pressure and shut the power to the pump down again. In another embodiment, controller  56  may be set up to turn off the pump if all valves are closed. The pressure switch may be used as a redundant device in such an embodiment. 
     In the preferred embodiment, each hose  24  is connected to a fuel outlet  22  by a dry connection  60  and to a cap  26  by a dry connection  62 . The hoses  24  may be 1 inch hoses and may have any suitable length depending on the well site set up. Having various lengths of hose  24  on board the trailer  14  may be advantageous. One or more spill containment pans (not shown) may be provided with the system, for example a pan of sufficient size to catch leaking fluids from the system during use. The pan or pans may be positioned to catch fluids leaking from each or both manifolds, and hose reels  30 . Each manifold may have a pan, or a single pan may be used for both manifolds. 
     In operation of a fuel delivery system to deliver fuel to selected fuel tanks of equipment at a well site during fracturing of a well, the method comprises pumping fuel from a fuel source such as the fuel source  14  through hoses  24  in parallel to each of the fuel tanks  12  and controlling fluid flow through each hose  24  independently of flow in other hoses  24 . Fluid flow in each hose  24  is controlled automatically or manually in response to receiving signals representative of fuel levels in the fuel tanks. Fuel spills at each fuel tank  12  are prevented by providing fuel flow to each fuel tank  12  through the fuel caps  26  on the fuel tanks  12 . Emergency shut down may be provided through the manually operated valves  28 . The caps  26  may be carried with the trailer  14  to a well site and the caps on the fuel tanks at the well site are removed and replaced with the caps  44 . The trailer  14  and any additional fuel sources remain on the well site throughout the fracturing job in accordance with conventional procedures. The emergency shut down may be provided for example to shut all equipment including valves and pumps, and may activate the positive air shutoff on the generator. 
     The number of outlets  22  on a manifold  36 ,  38  may vary and depends largely on space restrictions. Five outlets  22  per manifold  36 ,  38  is convenient for a typical large fracturing job and not all the outlets  22  need be used. Using more than one manifold permits redundancy in case one manifold develops a leak. The hoses  24  are run out to equipment  10  through an opening in the trailer wall in whatever arrangement the well operator has requested that the fracturing equipment be placed around the well. For example, one manifold  36  may supply fluid to equipment  10  lined up on one side of a well, while another manifold  38  may supply fluid to equipment  10  lined up on the other side. The hoses  24  may be conventional fuel delivery hoses, while other connections within the trailer  14  may be hard lines. The trailer  14  may be of the type made by Sea-Can Containers of Edmonton, Canada. The fuel sources  18 ,  20  may be loaded on a trailer separate from the trailer  14  and may constitute one or more body job tanker trucks or other suitable tanker or trailer mounted fuel tank for the storage of fuel. The fuel sources  18 ,  20  may be stacked vertically on the trailer  14  or arranged side by side depending on space requirements. The fuel sources  18 ,  20 , etc., should be provided with more than enough fuel for the intended fracturing job. For some fracturing jobs, two 4500 liter tanks might suffice, such as two Transtank Cube 4s (trademark) available from Transtank Equipment Solutions. 
     The control station  56  may be provided with a full readout or display for each fuel tank  12  being filled that shows the level of fuel in the fuel tank  12  including when the fuel tank  12  is near empty and near full. An alternative is to provide only fuel empty (low sensor dry) or fuel full (high sensor wet) signals. The fuel level sensor  54  may be provided with power from a generator or generators in series (not shown) on the trailer  14  (not preferred), via a battery installed with the sensor  54  or directly from a battery (not shown) on the equipment  12 . If a battery is used, it may need to be small due to space constraints on the cap  44 . Various types of fuel sensor may be used for the fuel sensor  54 . A float sensor is considered preferable over a transducer due to reliability issues. As shown schematically in  FIG. 2 , the fuel inlet on the fuel tank  12  is oriented at an angle to the vertical, such as 25°. Fuel level sensor  54  may be a hydrostatic pressure mechanism that references ambient atmospheric pressure as the base, and thus can operate at any altitude. Hydrostatic pressure sensors may be more robust than transducer systems and may have a sensing portion inserted into the fuel tank on a cable (not shown) depending downward from the fuel cap  26 . If the failsafe is set to “close”, all systems may need to be functioning in order for this system to give a reading. The operator can then tell immediately whether the system is functioning or not and take proactive steps to resolve any issue. No fuel may flow unless all systems are operating properly. Fuel requirements of a fuel tank  12  may be logged at the control station  56  to keep track of the rate at which the individual pieces of equipment  10  consume fuel. A, a filler or resin may be used in the electronic fittings (not shown) in the sensor  54  head for preventing liquid entry into the electronic components such as the wireless transceiver  55 . 
     The manual valves  28  should be readily accessible to an operator on the trailer  14 . This can be arranged with the manifolds  36 ,  38  mounted on a wall of the trailer with the outlets  22  extending inward of the trailer wall. Pressure gauges (not shown) may be supplied on each of the outlets  22 , one on the manifold side and one downstream of the valve  28 . As fuel levels in the fuel tanks  12  drop, a pressure differential between the pressure gauges can be used to determine a low fuel condition in the fuel tanks  12  and the fuel tanks  12  may be individually filled by an operator. During re-fueling at a fracturing job, the manual valves  28  may remain open, and the operator may electrically signal the automatic valves  58  to open, using an appropriate console (not shown) linked to the valves  58 . The level sensor  54  at the fuel tank  12  may be used to indicate a high level condition. An automatic system may be used to close the valves  58  automatically in the case of a high fluid level detection or the operator may close the valves  58  using the console (not shown). In the case of solenoid valves being used for the valves  58 , either cutting or providing power to the valves  58  may be used to cause the closing of the valves  58 , depending on operator preference. A screen or filter may be provided upstream of the solenoids, in order to prevent debris from entering and potentially damaging the solenoid. 
     Hoses from the outlets  22  may be stored on reels  30  mounted on two or more shelves within the trailer  14 . Filters (not shown) may be provided on the lines between the fuel sources  18 ,  20  and the pumps  32 ,  34 . An example of a suitable filter is a five-micron hydrosorb filter. Another example of a filter is a canister-style filter added immediately after the pump. A fuel meter (not shown) may also be placed on the lines between the fuel sources  18 ,  20  and the pumps  32 ,  34  so that the operator may determine the amount of fuel used on any particular job. The pumps  32 ,  34  and electrical equipment on the trailer  14  are supplied with power from a conventional generator or generators (not shown), which may conveniently be mounted on the trailer. Size of the pumps  32 ,  34  should be selected to ensure an adequate fill time for the fuel tanks  12 , such as 10 minutes, with the generator or generators (not shown) to supply appropriate power for the pumps and other electrically operated equipment on the trailer  14 . Pumps  32 ,  34  may be removable in order to be changed out if required. For example, the pumps  32 ,  34  may be connected by non-permanent wiring. Pumps  32 ,  34  may be centrifugal pumps, such as Gorman-Rupp™ or Blackmer™ pumps. Lights and suitable windows in the trailer  14  are provided so that the operator has full view of the equipment mounted on the trailer and the equipment  10  being refueled. The spatial orientation of the control station  56 , reels  30 , manifolds  36 ,  38 , tanks  18 ,  20  and other equipment such as the generators is a matter of design choice for the manufacturer and will depend on space requirements. 
     Preferably, during re-fueling of the fracturing equipment, fracturing equipment should not be pressurized and the fuel sources should not be located close to the fracturing equipment. Additional mechanical shut-off mechanisms may also be included, such as a manual shut-off on the remote ends of the hoses, for example at the dry connection  62 . Hydro-testing may be carried out on all elements of the system, including the manifolds and piping. Hydro-testing may be carried out at a suitable time, for example at time of manufacture or before each use. For example, the system may be pressured up and left overnight to check for leakage. In addition, quality control procedures may be carried out, for example including doing a diesel flush in the system to clear all debris. A compressor (not shown) or source of compressed fluid such as inert gas may be provided for clearing the lines and the system of fuel before transport. In another embodiment, the pumps  32 ,  34  may be used to clear the lines, for example by pumping pumps  32 ,  34  in reverse to pull flow back into the tanks  18 ,  20 . 
     Referring to  FIGS. 4-5 , a top end  46  for another embodiment of a fuel cap  26  is illustrated. The fuel cap  26  assembly illustrated in  FIG. 5  may be adapted to connect to the respective fuel tank  12  through a quick-connect coupling  47 , which may comprise a camlock  53 . In some cases the top end  46  may quick connect directly to the fuel tank  12 . In other embodiments such as the one shown in  FIG. 5 , the housing  43  comprises a bottom end  57  adapted to connect to the fuel tank  12  for example by threading to a fill riser  59  of fuel tank  12 . The bottom end may be provided in different sizes, for example to accommodate a 2″ or 3″ opening in the fuel tank or different designs of fill risers  59  such as a Freightliner™ lock top, and also a Peterbilt™ draw tight design. The top end  46  may be connected to the bottom end  57  directly or indirectly through quick connect coupling  47 . Moreover, the housing  43  may further comprise an intermediate portion  61  between top end  46  and bottom portion  61 . Intermediate portion  61  may be threaded to the top end  46  and connected to the bottom end  57  through the quick connect coupling  47 . Although intermediate portion  61  is shown in  FIG. 5  as being removably attached to top end  46 , in some cases intermediate portion  61  may be permanently or semi-permanently attached to top end  46  for rotation. Such a rotatable connection between portion  61  and top end  46  may be adapted to channel pressurized fluids under seal, which may be achieved with one or more bearings and dynamic seals (not shown), for example much like the rotatable connection between a fuel hose and hand held fuel dispenser at a fuel service station. In other cases bottom end  57  and top end  46  may connect to fill riser  59  much like a garden hose, with bottom end  57  provided as a threaded collar that seals against a flange at a bottom end of top end  46  through an o-ring seal (not shown). 
     Quick connect coupling  47  may comprise an annular bowl  63  shaped to couple with camlock  53 . Annular bowl  63  may be used with other quick connection couplings, and allows top end  46  to be installed at any desired radial angle. An o-ring  65  may be present in bottom end  57  for sealing against intermediate portion  61  upon locking of camlock  53 . One or more of ports  48 ,  49 , and  50  may be in a lateral surface  67 , such as an annular surface as shown, of top end  46 . As shown in  FIG. 4 , ports  48  (breather port) and  50  (fuel port) are in lateral surface  67 . One or more of ports  48 ,  49 , and  50  may be in a top surface  69  of top end  46  ( FIG. 5 ). Fuel cap  26  may be adapted to connect to male or female connections on fuel tank  12 . 
     Referring to  FIG. 5 , fuel cap  26  may comprise an overfill prevention valve  71 . Valve  71  may provide independent protection or redundant overfill protection with fuel level sensor  54  ( FIG. 2 ). Valve  71  may be directly or indirectly connected to port  50 , for example as part of a drop tube  73  assembly. Valve  71  may comprise a float-operated overfill shut off system, for example using one or more floats  75  connected to release one or more flaps  77  to block input fuel flow through drop tube  73  after fuel in tank  12  has reached a predetermined level or levels. The valve  71  illustrated in  FIG. 5  is similar to the twin flap system commonly used in underground storage tanks (USTs). Other overfill valve systems may use for example time domain reflectometry or contact sensors to ensure that fuel tank  12  is not overfilled. 
     A cabin (not shown) may be added to the system, for example comprising a heater, desk, and access to relevant control equipment. The cabin may have a window with a line-of-sight to the frac equipment. A dashboard may be visible from the cabin, the dashboard containing readouts of system characteristics such as fuel tank  12  levels. A gas detection system (not shown) may be used to detect the presence of leaking gas. In some embodiments, one or more of the hoses  24  may be provided with an auto nozzle fitting attachment to fill pieces of equipment other than fuel tank  12 , in order to obviate the need for an on-site fuel source other than the fuel system disclosed herein. An electrical box (not shown) may be mounted on the skid or trailer with rubber or resilient mounts to reduce vibrational issues. 
     Some types of equipment such as frac pumpers have two tanks, which may be connected by equalization lines. In such cases, fuel cap  26  may be connected into the tank  12  opposite the tank  12  under engine draw, in order to reduce the turbulence caused by fuel filling which may cause air to be taken into the fuel intake, which may affect the performance of the pumper. The return flow from the engine generally goes into the opposite tank from which fuel is drawn.