Patent Publication Number: US-10773820-B2

Title: Liquid tank system with over pressure protection

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. non-provisional patent application Ser. No. 15/277,640, filed on Sep. 27, 2016. 
    
    
     TECHNICAL FIELD 
     The present application related to liquid tank systems used in attitude change applications. 
     BACKGROUND OF THE ART 
     Liquid tanks may conventionally be provided with vents to regulate pressure and/or to avoid an over-pressurization of the tank. However, when liquid tanks undergo significant attitude variations, the vents may become submerged by the liquid, which impedes the normal operation of the vents and may thus impact the pressure regulation or over-pressurization protection. Hence, the attitude envelope capability of some apparatuses may be affected by these tank pressurization issues. Among the solutions used to address attitude envelope limitations are that tank volumes have been increased and/or complex mechanisms such as flip-flop valves have been developed. 
     SUMMARY 
     In one aspect, there is provided a liquid tank system comprising: a main liquid tank, at least an outlet communicating between a fluid circuit and the main liquid tank, at least one inlet communicating between the fluid circuit and the main liquid tank, an auxiliary cavity, a first vent passage communicating between the main liquid tank and the auxiliary cavity and configured to allow liquid and gas to flow at least from the main liquid tank to the auxiliary cavity, and at least one second vent passage communicating between the main liquid tank and the auxiliary cavity and configured to allow liquid and gas to flow at least from the main liquid tank to the auxiliary cavity, the at least one second vent passage having a flow control device configured to regulate flow through the at least one second vent passage, the flow control device having a set point at which it allows liquid and gas to flow from the main liquid tank to the auxiliary cavity only when a pressure in the main liquid tank is beyond a threshold, the liquid and gas flowing through the first vent passage below the threshold, wherein the liquid tank system has an attitude envelope in which the liquid tank system is configured such that, in use, the flow control device blocks flow through the at least one second vent passage when an end of the first vent passage in the main liquid tank is above a liquid level, and the flow control device allows gas and/or fluid flow through the at least one second vent passage when main fluid tank pressure is above the threshold and the end of the first vent passage in the main liquid tank is below the liquid level. 
     In another aspect, there is provided a method for reducing a gas pressure in a main liquid tank in fluid communication with an auxiliary cavity by a first vent passage and at least a second vent passage, comprising: venting the main liquid tank with the first vent passage and blocking the at least one second vent passage with a flow control device when an end of the first vent passage in the main liquid tank is above a liquid level, and opening the flow control device to allow gas or liquid flow through the at least one second vent passage when pressure in the main liquid tank is above a pressure threshold and the end of the first vent passage in the main liquid tank is below a liquid level. 
     In a further aspect, there is a liquid tank system comprising: a main liquid tank, at least an outlet communicating between a fluid circuit and the main liquid tank, at least one inlet communicating between the fluid circuit and the main liquid tank, an auxiliary cavity, a first vent passage communicating between the main liquid tank and the auxiliary cavity configured for liquid and gas to flow at least from the main liquid tank to the auxiliary cavity, and at least one second vent passage communicating between the main liquid tank and the auxiliary cavity and configured for liquid and gas to flow at least from the main liquid tank to the auxiliary cavity, the at least one second vent passage having a flow control device configured to regulate flow the at least one second vent passage, the flow control device having a set point at which it allows liquid and gas to flow from the main liquid tank to the auxiliary cavity only when a pressure in the main liquid tank is beyond a threshold, the liquid and gas flowing through the first vent passage below the threshold, wherein the liquid tank system has an attitude envelope in which the liquid tank system, in use, is vented in three modes, a first mode in which the flow control device blocks the at least one second vent passage with when an end of the first vent passage in the main liquid tank is above the liquid level, a second mode in which the flow control device allows gas flow through the at least one second vent passage when the end of the first vent passage in the main liquid tank is below the liquid level, and a third mode in which the flow control device allows liquid flow through the at least one second vent passage when liquid pressure is above the threshold and the end of the first vent passage in the main liquid tank is below the liquid level. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1  is a schematic view of a liquid tank system with over pressure protection in accordance with the present disclosure; 
         FIG. 2A  is a schematic view of the liquid tank system of  FIG. 1  in a first mode of operation, the liquid tank system being in a vertical orientation; 
         FIG. 2B  is a schematic view of the liquid tank system of  FIG. 1  in the first mode of operation, the liquid tank system being in a horizontal orientation; 
         FIG. 3A  is a schematic view of the liquid tank system of  FIG. 1  in a second mode of operation, the liquid tank system being in a vertical orientation; 
         FIG. 3B  is a schematic view of the liquid tank system of  FIG. 1  in the second mode of operation, the liquid tank system being in a horizontal orientation; 
         FIG. 4A  is a schematic view of the liquid tank system of  FIG. 1  in a third mode of operation, the liquid tank system being in a vertical orientation; and 
         FIG. 4B  is a schematic view of the liquid tank system of  FIG. 1  in the third mode of operation, the liquid tank system being in a horizontal orientation. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings and more particularly to  FIG. 1 , a liquid tank system in accordance with the present disclosure is generally shown at  10 . The liquid tank system  10  may be part of a closed loop system storing a liquid to be supplied to components of a fluid system. The liquid may then be returned to the liquid tank system  10  as part of the closed loop. In an embodiment, the liquid may be oil used for lubricating purposes, but other types of liquid may be used, such as fuel. 
     By way of example, the liquid tank system  10  has an outlet  11  in which a main pump  12  pumps the liquid to components  13 —the expression outlet is used as it is the passage through which the liquid exits the tank system  10 , but it may also be known as an inlet in other circumstances. The liquid tank system  10  may also have an outlet  14  in which a scavenge pump  15  collects and directs to an inlet  16  of the liquid tank system  10 —the expression inlet is used as it is the passage through which the liquid exits the tank system  10 , but it may also be known as an outlet in other circumstances. The liquid tank system  10  is part of an apparatus that has an attitude envelope, whereby the liquid tank system  10  may be said to operate in an attitude envelope. The attitude envelop is the attitude range in which the liquid tank system  10  is rated to operate, in spite of orientation variations of the apparatus. 
     For example, the liquid tank system  10  may be used in aerobatic planes, in tilt rotors, known to operate in large attitude envelopes in contrast to other aircraft. 
     However, the liquid tank system  10  may also be found in other types of apparatuses or vehicles, such as all-terrain vehicles, watercraft, to name but a few examples, especially those that operate in an attitude envelope. 
     The liquid tank system  10  has a main tank  20 , and auxiliary tank or cavity  30 , a first vent passage  40 , and one or more secondary vent passage  50 . 
     The main tank  20  is used as storage for the liquid. The main tank  20  is a closed cavity of fixed volume (a.k.a., fixed size liquid tank), i.e., it is not an open tank. The auxiliary tank  30  provides auxiliary storage capacity in the event of over pressurization of the main tank  20 , as described hereinafter. In an embodiment, the auxiliary tank  30  may be part of a component using the liquid, such as a gear box (e.g., auxiliary gear box) and may be vented. Even though the auxiliary tank  30  is referred to as a tank, it may be a sealed cavity that is part of the main tank  20 , with flow from the tank  20  to the tank  30  permitted only through the vent passages  40  and  50 . 
     The vent passages  40  and  50  are used to regulate pressure in the main tank  20 , and to relieve the main tank  20  from over pressurization when necessary. The vent passages  40  and  50  therefore allow fluid flow from the main tank  20  to the auxiliary tank  30 , and may be provided with flow restricting devices in order to control, regulate and/or limit the flow from the tank  20  to the tank  30  according to modes of operation described hereinafter. 
     The first vent passage  40  may be an open passage having an inlet end  40 A in the main tank  20 , and an outlet end  40 B in the auxiliary tank  30 . By open passage, the first vent passage  40  may be continuously or permanently open, in that it does not have any obstruction selectively blocking its channel. The first vent passage  40  may also have a controlled orifice  41 , valve(s) or like flow control devices between the ends  40 A and  40 B to control the flow rate through the first vent passage  40 . The secondary vent passage  50  also defines a passage from the main tank  20  to the auxiliary tank  30 , with an inlet end  50 A in the main tank  20 , and an outlet end  50 B in the auxiliary tank  30 . The secondary vent passage  50  may have a controlled orifice  51 , valve(s)  52  or like flow control devices to control the flow rate through the secondary vent passage  50 . The valve  52  is selected to have a set point related to an opening or cracking pressure that is higher than a pressure at which flow normally occurs in the first vent passage  40 , so as to selectively open when pressure in the main tank  20  is only above a given pressure threshold. The flow control device  52  may be any type of valve, such as a check valve, a solenoid valve, an electronic valve etc, configured to automatically open when a pressure threshold is reached. The flow control device  52  may open progressively or not. 
     For example, in an embodiment, the first vent passage  40  is configured to allow free flow of fluids between the tanks  20  and  30 , whereas the second vent passage  50  only allows flow of fluids from the tank  20  to the tank  30  when a threshold fluid pressure is reached in the tank  20 , to relieve the tank  20  from over pressure. Even though  FIG. 1  shows a single secondary vent passage  50 , two or more of the secondary vent passage  50  may be present in the liquid tank system  10 , to increase the coverage of pressure relief and thus the attitude envelope of the liquid tank system  10 . 
     The vent passages  40  and  50  are located and configured to enable three distinct modes of pressure regulation for the liquid tank system  10 , within the attitude envelope, to avoid over pressurization of the main tank  20  in spite of attitude changes of the main tank  20 . The vent passages operate independently from each other using different cracking pressures and therefore open sequentially depending on the pressure. 
     Referring to  FIGS. 2A and 2B , a first of three modes is shown,  FIGS. 3A-3B  showing a second mode and  FIGS. 4A-4B  showing a third mode. The monikers “first”, “second” and “third” are simply used to distinguish the modes from one another. For convention, the liquid level in the main tank  20  is shown at L, with a gas pocket being above the liquid level L. Although the expression “gas pocket” is used, the gas above the liquid level L may contain some vapour. In the attitude envelope of the liquid tank system  10 , there must be sufficient liquid for the main pump  12  to supply fluid to the components  13  as required. Accordingly, as observed in  FIGS. 2A-4B , the outlet  11  is under the liquid level L, regardless of the attitude of the liquid tank system  10 , although the outlet  11  may be occasionally over the liquid level L, such as in a negative g condition. 
     Moreover,  FIGS. 2A, 3A and 4A  all show the main tank  20  in its vertical orientation, whereas  FIGS. 2B, 3B and 4B  all show the main tank  20  in a horizontal orientation, yet within the attitude envelope of the main tank  20 . Moreover, for simplicity, the outlet ends  40 B and  50 B are not shown in  FIGS. 2A-4B , but are present in the manner shown in  FIG. 1 . 
     First Mode 
     In  FIG. 2A , both of the inlets  40 A and  50 A are above the liquid level L. Therefore, the gas pocket is in fluid communication with the auxiliary tank  30  via the first vent passage  40 . As a result, the gas pressure in the main tank  20  is maintained below the threshold pressure, and the secondary vent passage  50  remains closed, no gas passing through the secondary vent passage  50 . 
     In  FIG. 2B , an attitude variation causes the liquid tank system  10  to be horizontal. The inlet  40 A remains above the liquid level L, but the inlet  50 A is now below the liquid level L, and is thus submerged in the liquid. Therefore, the gas pocket is in fluid communication with the auxiliary tank  30  via the first vent passage  40 . As a result, the gas pressure in the main tank  20  is maintained below the threshold pressure, and the secondary vent passage  50  is consequentially shut, no liquid passing through the secondary vent passage  50 . 
     The first vent passage  40  is positioned in the tank  20  such that, when the inlet end  40 A is in the gas pocket, the secondary vent passage(s)  50  is blocked by the flow control device  52 . For example, the position is such that the gas pocket is large enough for the venting capacity of the first vent passage  40 , the first vent passage  40  handling the venting without assistance from the secondary vent passage(s)  50 . 
     Second Mode 
     In  FIG. 3A , the inlet  40 A is now below the liquid level L, and is thus submerged in the liquid, whereas the inlet  50 A remains above the liquid level L. The first vent passage  40  may allow liquid to pass therethrough to reach the auxiliary tank  30 , and hence lower the liquid level L. The gas pocket may be in fluid communication with the auxiliary tank  30  via the secondary vent passage  50 . If the pressure of the gas pocket reaches the pressure threshold, the flow control device  52  opens to relieve the main tank  20 . As a result, the main tank  20  is vented by the secondary vent passage  50  acting as pressure-relief mechanism. In the second mode, when the inlet end  40 A is submerged as in  FIG. 3A , the volume of the gas pocket is increased while excess pressure is being vented via the secondary vent passage  50 , by the first vent passage  40 &#39;s ability to allow fluid flow to the auxiliary tank  30 . 
     In  FIG. 3B , an attitude variation causes the liquid tank system  10  to be horizontal. The inlet  40 A is now above the liquid level L, but the inlet  50 A is now below the liquid level L, and is thus submerged in the liquid. Therefore, the gas pocket is in fluid communication with the auxiliary tank  30  via the first vent passage  40 . As a result, the gas pressure in the main tank  20  is maintained below the threshold pressure by venting via the first vent passage  40 , and the secondary vent passage  50  is consequentially shut, with no liquid passing through the secondary vent passage  50 . 
     Third Mode 
     In  FIG. 4A , both of the inlets  40 A and  50 A are below the liquid level L, and are thus submerged in the liquid. With such high liquid level, the volume available for the gas pocket is reduced, resulting in an increased gas pressure, and increased liquid pressure. Both of the vent passages  40  and  50  may allow liquid to pass therethrough to reach the auxiliary tank  30  (if the cracking point is reached for the device  52 ), and hence lower the liquid level L, until one of the inlets  40 A and  50 A is below the liquid level L and vents the main tank  20 . The auxiliary tank  30  is therefore used as temporary liquid storage to reduce the pressure in the main tank  20 . 
     In  FIG. 4B , an attitude variation causes the liquid tank system  10  to be horizontal. Hence, as in  FIG. 4A , both of the inlets  40 A and  50 A are below the liquid level L, and are submerged in the liquid. Again, the volume available for the gas pocket is reduced, resulting in an increased gas pressure, and increased liquid pressure. Both of the vent passages  40  and  50  allow liquid to pass therethrough to reach the auxiliary tank  30 , and hence lower the liquid level L, until one of the inlets  40 A and  50 A is below the liquid level L and vents the main tank  20 . 
     The liquid tank system  10  may have more than one of the secondary vent passages  50 , independent from one another. The secondary vent passages  50  would have their inlet ends  50 A strategically positioned at various locations in the main tank  20  to limit the instances in which all vents are submerged as in  FIGS. 4A and 4B . For example, in  FIG. 4B , the inlet end of another of the secondary vent passages  50  could be located at  50 A′, to act as a vent while the inlet ends  40 A and  50 A are submerged. The inlet end  50 A′ would be related to a flow control device (such as valve  52 ) having a cracking point above the operating pressure of the first vent passage  40 . The cracking point of valves  52  of the two secondary vent passages  50  may be the same or different. Inlet ends  50 A/ 50 A′ of the secondary vent passages  50  are therefore strategically positioned to cover complementary parts of the main tank  20 , such that when one of the inlet ends  50 A is submerged below the liquid level L simultaneously with the inlet end  40 A, the other inlet end  50 A′ serves for overpressure protection. This may be described relative to the attitude envelope of the liquid tank system  10 . It is first assumed that the liquid tank system  10  is at opposed end orientations of the attitude envelope in  FIG. 4A  (vertical orientation) and  FIG. 4B  (horizontal orientation). If the attitude envelope were divided in two parts, the vertical orientation (at a first end orientation) would be in a first part, and the horizontal orientation (at the second end orientation) would be in the second part. The vent passages  50  are arranged such that one inlet end  50 A serves as vent or pressure-relief mechanism in the first part of the attitude envelope (a.k.a., first range of attitudes), and the other inlet end  50 A′ serves as vent or pressure-relief mechanism in the second part of the attitude envelope (a.k.a., second range of attitudes). The first part of the attitude envelope or first range of attitudes does not overlap the second part of the attitude envelope or second range of attitudes, they are separate and distinct from one another. Accordingly, the presence of a plurality (more than one) secondary vent passage  50  allows operation of the liquid tank system  10  in the second mode rather than in the third mode. 
     The attitude envelope capability may be adjusted by adjusting some of the parameters and size of the liquid tank system  10 . For example, the number of vent passages, the position of the inlet ends of the vent passages in the main tank  20 , the opening and/or cracking pressure of the flow control devices and the number of control orifices, and the pressure threshold. 
     Accordingly, the presence of the vent passages  40  and  50  in the manner described above may increase the attitude envelope capability and capacity of a liquid tank, in comparison to liquid tanks of similar volume, without the arrangement of vent passages  40  and  50  described herein. The multiple vent passages are located at specific locations in the tank to regulate the tank pressure within the entire attitude envelop by either controlling the gas flow or the amount of liquid transferred to the vented auxiliary cavity  30 . The three modes automatically switch from one to the other, as a function of the attitude of the main tank  20  and of the liquid level in the tank, without requiring any human intervention. The use of the liquid tank system  10  may result in a smaller and lighter apparatuses, in comparison to apparatuses having an equivalent attitude envelope, but no vent passage arrangement as in the liquid tank system  10 . 
     Therefore, the liquid tank system  10 , or like tank system may operate in the following method for reducing a gas pressure in the main liquid tank  20 : The outlet  11  of the main liquid tank  20  is continuously maintained below a liquid level in an attitude envelope of the main liquid tank  20 , but with exception such as in a negative g condition. The main liquid tank  20  is vented with the first vent passage  40  and the secondary vent passage  50  is blocked with the flow control device  52  when the inlet end  40 A of the first vent passage  40  is above a liquid level L in the main liquid tank  20 . The flow control device  52  is opened to allow gas or liquid flow through the secondary vent passage(s)  50  when gas pressure in the main liquid tank  20  is above a pressure threshold and the inlet end  40 A of the first vent passage  40  is below the liquid level L. 
     The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, the system described above may be applied to gas turbine engines, such as those for aerobatic planes, tilt rotors, or any other apparatus or vehicle configured to operate in attitude changes. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.