Expansion device

Abstract

To provide an expansion device that is configured compact in size and capable of effectively preventing an abnormal rise in pressure within the expansion device caused by the differential pressure across the expansion device. An expansion device according to the present invention cancels part of refrigerant pressure by a pressure-canceling structure. More specifically, by the amount of pressure received by a valve-closing pressure-receiving surface, the elastic force required of a spring can be reduced. As a result, a small-sized spring can be employed as the spring, and the entire expansion device can be made compact in construction. Further, when the differential pressure across the expansion device has become equal to or higher than a predetermined value, a relief mechanism enables refrigerant flowing in from the upstream side to escape into a passage other than a refrigerant passage through a valve element. This makes is possible to prevent an abnormal rise in the refrigerant pressure inside the expansion device, thereby preventing breakage or the like of the internal components.

1 . An expansion device that is disposed in a flow passage of refrigerant circulating through a refrigeration cycle, for passing the refrigerant introduced from an upstream side thereof through an internal refrigerant passage thereof to thereby cause decompression of the refrigerant and allow the decompressed refrigerant to flow downstream, and is equipped with a relief mechanism that is operable when a differential pressure across the expansion device has become equal to or higher than a predetermined value, to open a flow passage other than the refrigerant passage which is closed by a valve element urged by an elastic member disposed within the expansion device, to thereby allow at least part of the refrigerant flowing in from the upstream side to escape via the flow passage to flow downstream, the expansion device comprising: 
 a pressure-cancelling structure that cancels part of pressure of the refrigerant acting on the valve element in a valve-opening direction.    
   
   
       2 . An expansion device that is disposed in a flow passage of refrigerant circulating through a refrigeration cycle, comprising: 
 a cylinder in the form of a hollow cylinder, the cylinder having a valve seat formed by a stepped portion provided inside the hollow cylinder;    a valve element that has a body in the form of a hollow cylinder, the valve element being movably inserted within the cylinder, and including a valve portion that forms part of the body and can be removably seated on the valve seat, and a refrigerant passage extending through an inside of the body to allow passage of the refrigerant;    a restriction mechanism that decompresses the refrigerant passing through the refrigerant passage;    an elastic member that is disposed within the cylinders for urging the valve element in a valve-closing direction;    a pressure-cancelling structure that cancels at least part of pressure of the refrigerant acting on the valve element in a valve-opening direction, the pressure-cancelling structure comprising a valve-closing pressure-receiving surface that receives pressure of the refrigerant acting on the valve element in the valve-closing direction and has a pressure-receiving area which is smaller than a pressure-receiving area of a valve-opening pressure-receiving surface that receives pressure of the refrigerant acting on the valve element in the valve-opening direction; and    a relief mechanism that is operable when a differential pressure across the expansion device has become equal to or higher than a predetermined value to cause the valve portion to be moved away from the valve seat, to allow at least part of the refrigerant flowing in from an upstream side to escape into a flow passage other than the refrigerant passage extending through the cylinder.    
   
   
       3 . The expansion device according to  claim 2 , wherein, the valve element includes a guided portion that is guided along an inner peripheral surface of the cylinder when the valve element is moved to and away from the valve seat.  
   
   
       4 . The expansion device according to  claim 2 , wherein the cylinder is directly fixed to an inside of the piping of the refrigeration cycle.  
   
   
       5 . The expansion device according to  claim 3 , comprising: 
 a stepped portion in the refrigerant passage of the valve element at which the refrigerant passage is expanded in an upstream-to-downstream direction;    an inner shaft member in the form of a hollow cylinder that has a flow-restricting portion formed therein, the flow-restricting portion having a cross-section smaller than a cross-section of the refrigerant passage, and is partially inserted into an expanded side of the stepped portion of the valve element, the inner shaft member protruding downstream from the valve element, and functioning as the restriction mechanism; and    a stopper that is fixed to the cylinder, and configured to be capable of having a downstream end of the inner shaft member engaged thereat, the stopper being formed with a through hole having a cross-section larger than a cross-section of the flow-restricting portion, and    wherein an internal space is formed between the inner shaft member and the stepped portion, and the stepped portion forms the valve-closing pressure-receiving surface.    
   
   
       6 . The expansion device according to  claim 5 , wherein the stopper is formed with at least one second through hole other than the through hole, the second through hole communicating with the flow passage other than the refrigerant passage, and 
 wherein a flow passage area of an entirety of the second through hole is larger than a flow passage area of a gap formed between the valve portion and the valve seat when the valve element is opened.    
   
   
       7 . The expansion device according to  claim 5 , wherein the inner shaft member is supported by the valve element, but not fixed to any part of an internal structure of the cylinder.  
   
   
       8 . The expansion device according to  claim 5 , wherein the cylinder includes a small pipe portion that communicates with the refrigerant passage when the valve element is seated on the valve seat, and a large pipe portion that has a passage cross-section larger than a passage cross-section of the small pipe portion, and is configured such that the stepped portion is formed by the small pipe portion and the large pipe portion, and 
 wherein the pressure-cancelling structure is formed by making the passage cross-section of the small pipe portion larger than a cross-section of the expanded side of the stepped portion of the valve element.    
   
   
       9 . The expansion device according to  claim 5 , wherein the guided portion comprises a plurality of protruding portions extending from the body toward an inner surface of the cylinder, the protruding portions defining therebetween refrigerant flow passages that allow passage of the refrigerant, and on the other hand, the stopper has at least one second through hole formed around the through hole, the second through hole communicating with the refrigerant flow passages, and 
 wherein when the valve portion is moved away from the valve seat, the relief mechanism allows at least part of the refrigerant flowing in from the upstream side to flow downstream via a gap between the valve portion and the valve seat, the refrigerant flow passages, and the second through hole.    
   
   
       10 . The expansion device according to  claim 5 , wherein the elastic member is interposed between the stopper and the valve element, 
 the expansion device comprising an adjusting mechanism that adjusts a position of the stopper within the cylinder, and    wherein an elastic force of the elastic member can be adjusted by adjusting the position of the stopper using the adjusting mechanism.    
   
   
       11 . The expansion device according to claim.  3 , wherein the cylinder comprises: 
 a valve seat portion in the form of a hollow cylinder that is fixed to an inside of the cylinder as a separate member, with one end thereof opening in an upstream direction, and an opposite end thereof being formed with the valve seat, the valve seat portion communicating with the refrigerant passage when the valve element is seated thereon;    a large pipe portion that has a passage cross-section larger than a passage cross-section of the valve seat portion, and has the valve portion inserted therein; and    a guide pipe portion that has the guided portion inserted therein such that the guided portion is slidably supported therein, and has a flow-restricting portion formed at a downstream end thereof, the flow-restricting portion functioning as the restriction mechanism, and    wherein the pressure-cancelling structure is formed by making the passage cross-section of the valve seat portion larger than a passage cross-section of the guide pipe portion.    
   
   
       12 . The expansion device according to  claim 11 , wherein the guide pipe portion and the large pipe portion are configured to define a refrigerant flow passage that allows passage of the refrigerant, between the guide pipe portion and the large pipe portion, and the piping of the refrigeration cycle, and 
 wherein the large pipe portion has a side wall formed with at least one communication hole for causing an inside thereof to communicate with the refrigerant flow passage, and    wherein the relief mechanism allows at least part of the refrigerant flowing in from the upstream side to flow downstream via a gap between the valve portion and the valve seat, the communication hole, and the refrigerant flow passage.    
   
   
       13 . The expansion device according to  claim 11 , comprising an adjusting mechanism that adjusts a position of the valve seat portion within the cylinder, and 
 wherein an elastic force of the elastic member can be adjusted via the valve element by adjusting the position of the valve seat portion using the adjusting mechanism.    
   
   
       14 . The expansion device according to  claim 3 , wherein the cylinder has an introducing hole formed through a side wall thereof, for allowing the refrigerant to be introduced therein, and includes a small pipe portion that slidably supports the guided portion, and a large pipe portion that has a passage cross-section larger than a passage cross-section of the small pipe portion, and has the valve portion inserted therein, and 
 wherein at a pipe portion of the valve element between the guided portion and the valve portion, a space portion is formed between the valve element and the small pipe portion, for communicating with the introducing hole, and    wherein the pipe portion has an orifice hole formed through a side wall thereof, the orifice hole communicating between the space portion and the refrigerant passage, and functioning as the restriction mechanism, and    wherein when the valve element is seated, the refrigerant flowing in via the piping of the refrigeration cycle is introduced into the refrigerant passage via the introducing hole and the orifice hole, and    wherein the pressure-canceling structure is formed by forming an expanded pipe portion in the small pipe portion, at a location in the vicinity of the valve seat.    
   
   
       15 . The expansion device according to  claim 14 , wherein the relief mechanism is operable when the valve portion is moved away from the valve seat, to allow at least part of the refrigerant flowing in from the upstream side to flow downstream via the space portion, and a gap between the valve portion and the valve seat.  
   
   
       16 . The expansion device: according to  claim 14 , comprising: 
 a stopper in the form of a hollow cylinder that is fixed to the cylinder, the elastic member being interposed between the stopper and the valve element;    an adjusting mechanism that adjusts a position of the stopper within the cylinder, and    wherein an elastic force of the elastic member can be adjusted by adjusting the position of the stopper using the adjusting mechanism.    
   
   
       17 . The expansion device according to  claim 2 , wherein the cylinder comprises a small pipe portion that communicates with the refrigerant passage when the valve element is seated on the valve seat, and a large pipe portion that has a passage cross-section larger than a passage cross-section of the small pipe portion, and has the valve element inserted therein, the small pipe portion and the large pipe portion forming the stepped portion, and 
 wherein, an upstream end of the valve element is configured such that the upstream end is fitted into the small pipe portion by a predetermined amount when the valve element is seated, and the upstream end has a side wall formed with at least one slit opening toward the small pipe portion, and    wherein the relief mechanism is configured such that when the valve portion is moved away from the valve seat, the slit progressively increases an opening that communicates between the small pipe portion and the large pipe portion, and when the upstream end of the valve element is removed from the small pipe portion, the opening is rapidly increased, thereby allowing at least part of the refrigerant flowing in from the upstream side to stepwise escape into the flow passage other than the refrigerant passage extending through the cylinder to thereby allow the refrigerant to flow downstream.    
   
   
       18 . The expansion device according to  claim 17 , comprising: 
 a stopper in the form of a hollow cylinder that is fixed to the cylinders, the elastic member being interposed between the stopper and the valve element;    an adjusting mechanism that adjusts a position of the stopper within the cylinder, and    wherein an elastic force of the elastic member can be adjusted by adjusting the position of the stopper using the adjusting mechanism.    
   
   
       19 . The expansion device according to  claim 2 , wherein the valve element having the pressure-cancelling structure, the elastic member urging the valve element, and the relief mechanism are provided in a plurality of stages, from the upstream side to a downstream side within the cylinder, and 
 wherein the relief mechanisms are configured to stepwise operate by adjusting respective elastic forces of the elastic members urging the valve elements.    
   
   
       20 . An expansion device that is disposed in a flow passage of refrigerant circulating through a refrigeration cycle, comprising: 
 a cylinder in the form of a hollow cylinder, the cylinder having a first valve seat formed by a stepped portion provided inside the hollow cylinder;    a first valve element that has a body in the form of a hollow cylinder inserted in the cylinder, and includes a valve portion that forms part of the body and can be removably seated on the first valve seat, a guided portion that is guided along an inner peripheral surface of the cylinder when the body is moved to and away from the first valve seat, and a first refrigerant passage that extends through an inside of the body and has a stepped portion formed therein at which the first refrigerant passage is expanded in an upstream-to-downstream direction, the first refrigerant passage allowing passage of the refrigerant;    a first elastic member that is disposed within the, cylinder, for urging the first valve element in a valve-closing direction;    a pressure-cancelling structure that cancels at least part of pressure of the refrigerant acting on the first valve element in a valve-opening direction, the pressure-cancelling structure, comprising a valve-closing pressure-receiving surface that receives pressure of the refrigerant acting on the first valve element in the valve-closing direction and has a pressure-receiving area smaller than a pressure-receiving area of a valve-opening pressure-receiving surface that receives pressure of the refrigerant acting on the first valve element in the valve-opening direction;    a first relief mechanism that is operable when a differential, pressure across the expansion device has become equal to or higher than a first predetermined value to cause the valve portion to be moved away from the first valve seat, to allow at least part of the refrigerant flowing in from an upstream side to escape into a flow passage other than the first refrigerant passage within the cylinder to thereby allow the refrigerant to flow downstream;    an inner shaft member in the form of a hollow cylinder that is formed therein with a flow-restricting portion having a cross-section smaller than a cross-section of the first refrigerant passage, and is partially inserted into an expanded side of the stepped portion of the first valve element, the inner shaft member protruding downstream from the first valve element;    an inner cylinder in the form of a hollow cylinder that is fixed to an inside of the cylinder, and has at least one slit formed through a side wall of an upstream end thereof, the upstream end being capable of having a downstream end of the inner shaft member engaged thereat, the inner cylinder being formed with a communication hole extending therethrough for communication with the flow-restricting portion;    a second valve element that has a body in the form of a hollow cylinder inserted in the inner cylinder, the second valve element including a valve portion that forms part of the body of the second valve element and can be removably seated on a second valve seat formed on a downstream end face of the inner shaft member, a guided portion that is guided along the communication hole when the body of the second valve element is moved to and away from the second valve seat, and a second refrigerant passage that extends through an inside of the body of the second valve element and has a cross-section smaller than the cross-section of the flow-restricting portion;    a second elastic member that is disposed within the inner cylinder, for urging the second valve element in a valve-closing direction; and    a second relief mechanism that is operable when the differential pressure across the expansion device has become equal to or higher than a second predetermined value smaller than the first predetermined value to cause the valve portion of the second valve element to be moved away from the second valve seat, to allow at least part of the refrigerant flowing in from the upstream side to escape into a flow passage other than the second refrigerant passage within the inner cylinder to thereby allow the refrigerant to flow downstream.    
   
   
       21 . The expansion device according to  claim 20 , wherein an amount of refrigerant allowed to escape by the first relief mechanism is larger than an amount of refrigerant allowed to escape by the second relief mechanism.  
   
   
       22 . The expansion device according to  claim 20 , wherein the first elastic member is interposed between the inner cylinder and the first valve element, 
 the expansion device comprising an adjusting mechanism that adjusts a position of the inner cylinder within the cylinder, and    wherein an elastic force of the first elastic member can be adjusted by adjusting the position of the inner cylinder using the adjusting mechanism.    
   
   
       23 . The expansion device according to  claim 20 , comprising: 
 a stopper in the form of a hollow cylinder that is fixed to the inner cylinder, the second elastic member being interposed between the stopper and the second valve element; and    a second adjusting mechanism that adjusts a position of the stopper within the inner cylinder, and    wherein an elastic force of the second elastic member can be adjusted by adjusting a position of the stopper using the second adjusting mechanism.    
   
   
       24 . The expansion device according to  claim 5 , wherein the valve element having the pressure-cancelling structure, the elastic member urging the valve element, the relief mechanism, the inner shaft member, and the stopper are provided in two stages, from the upstream side to a downstream side within the cylinder, and 
 wherein a valve seat is formed on a downstream end face of the stopper interposed between the two valve elements, for allowing a valve portion of the valve element on a downstream side to be seated thereon,    wherein the elastic members are interposed between the stoppers and the valve elements, respectively,    the expansion device comprising adjusting mechanisms that adjust respective positions of the stoppers within the cylinder, and    wherein elastic forces of the elastic members can be adjusted by adjusting the positions of the stoppers using the adjusting mechanisms, respectively.    
   
   
       25 . The expansion device according to  claim 2 , wherein, the cylinder includes a small pipe portion that communicates with the refrigerant passage when the valve element is seated on the valve seat, and a large pipe portion that has a passage cross-section larger than a passage cross-section of the small pipe portion, and has the valve element inserted therein, the stepped portion being formed by the small pipe portion and the large, pipe portion, and 
 wherein when the valve element is seated, an upstream end of the valve element is inserted into the small pipe portion with a predetermined spacing from an inner wall of the small pipe potion, and    wherein when the valve portion is moved away from the valve seat, until the upstream end of the valve element is removed from the small pipe portion, the relief mechanism allows part of the refrigerant flowing in from the upstream side to leak via the gap, and when the upstream end of the valve element has been removed from the small pipe portion, the relief mechanism allows the refrigerant to escape at a larger flow rate, whereby the refrigerant is allowed to stepwise escape into the flow passage other than the refrigerant passage through the cylinder to thereby allow the refrigerant to flow downstream.    
   
   
       26 . The expansion device according to  claim 25 , comprising: 
 a stopper in the form of a hollow cylinder that is fixed to the cylinder, the elastic member being interposed between the stopper and the valve element;    an adjusting mechanism that adjusts a position of the stopper within the cylinder, and    wherein an elastic force of the elastic member can be adjusted by adjusting the position of the stopper using the adjusting mechanism.    
   
   
       27 . The expansion device according to  claim 2 , wherein the valve element has a side wall formed with at least one communication hole for communicating between an inside and an outside of the refrigerant passage, and 
 wherein the relief mechanisms includes a flow passage-switching structure that switches between flow passages of the refrigerant by opening or closing the communication hole according to movement of the valve element.    
   
   
       28 . The expansion device according to  claim 27 , wherein the cylinder includes a small pipe portion that communicates with the refrigerant passage when the valve element is seated on the valve seat, and a large pipe portion that has a passage cross-section larger than a passage cross-section of the small pipe portion, and has the valve element inserted therein, the stepped portion being formed by the small pipe portion and the large pipe portion, and 
 wherein an upstream end of the valve element is inserted inside an inner wall of the small pipe portion by a predetermined amount when the valve element is seated, and    wherein the relief mechanism opens the communication hole to allow the refrigerant to escape, when the valve element is seated, and    the relief mechanism keeps the communication hole closed until the upstream end is removed from the small pipe portion, when the valve portion is moved away from the valve seat, and    wherein when the upstream end of the valve element is moved away from the small pipe portion, at least part of the refrigerant flowing in from the upstream side is allowed to escape into the flow passage other than the refrigerant passage through the cylinder to flow downstream.    
   
   
       29 . The expansion device according to  claim 27 , comprising: 
 a stopper in the form of a hollow cylinder that is fixed to the cylinder, the elastic member being interposed between the stopper and the valve element;    an adjusting mechanism that adjusts a position of the stopper within the cylinder, and    wherein an elastic force of the elastic member can be adjusted by adjusting the position of the stopper using the adjusting mechanism.    
   
   
       30 . The expansion device according to  claim 5 , wherein the valve element having the pressure-cancelling structure, the elastic member urging the valve element, and the relief mechanism, the inner shaft member, and the stopper are provided in a plurality of stages, from the upstream side to a downstream side within the cylinder, 
 wherein on a downstream end face of one of the stoppers interposed between the valve elements, there is formed a valve seat for allowing the valve portion of one of the valve elements on a downstream side of the stopper to be seated thereon,    wherein the elastic members are interposed between the stoppers and the valve elements, respectively,    the expansion device comprising adjusting mechanisms that adjust positions of the stoppers within the cylinder, respectively,    the relief mechanisms are configured to sequentially operates from the downstream side, in a stepwise manner, by adjusting elastic forces of the elastic members by adjusting the positions of the stoppers, using the adjusting mechanisms, respectively, and    wherein the valve element on the downstream side has a side wall formed with at least one communication hole for communicating between an inside and an outside of the refrigerant passage, and    wherein a flow passage-switching structure is provided which switches the flow passage of the refrigerant by opening or closing the communication hole according to the movement of the valve element formed with the communication hole.    
   
   
       31 . The expansion device according to  claim 30 , wherein the flow passage-switching mechanism causes the communication hole to be once closed during a process of rise in the differential pressure across the expansion device.  
   
   
       32 . An expansion device that is disposed in a flow passage of refrigerant circulating through a refrigeration cycle, comprising: 
 a cylinder in the form of a hollow cylinder that has a valve seat formed therein;    a valve element that has a body in the form of a hollow cylinder that is movably inserted in the cylinder and can define a refrigerant passage for allowing passage of refrigerant through the cylinder, the body having a portion forming a valve portion that can be moved to and away from the valve seat;    a restriction mechanism that decompresses the refrigerant passing through the refrigerant passage;    an elastic member that is disposed within the cylinder, for urging the valve element in a valve-closing direction;    a pressure-cancelling structure that cancels part of pressure of the-refrigerant acting on the-valve element in a valve-opening direction, the pressure-cancelling structure comprising a valve-opening pressure-receiving surface that receives pressure of the refrigerant acting on the valve element in the valve-opening direction, and a valve-closing pressure-receiving surface that receives pressure of the refrigerant acting on the valve element in the valve-closing direction; and    a relief mechanism that is operable when the differential pressure across the expansion device has become equal to or higher than a predetermined value to cause the valve portion to be moved away from the valve seat, to open a flow passage other than the refrigerant passage extending through the cylinder by way of the restriction mechanism, to thereby allow at least part of the refrigerant flowing in from the upstream side to escape into the flow passage other than the refrigerant passage to flow downstream.    
   
   
       33 . The expansion device according to  claim 32 , wherein the valve seat is formed by a stepped portion formed inside the cylinder, and the valve-opening pressure-receiving surface and the valve-closing pressure-receiving surface of the valve element are both formed on an upstream side of the restriction mechanism, and 
 wherein the restriction mechanism is formed by a gap between a reduced pipe portion provided downstream of the body of the valve element, and a shaft-like member partially inserted into the reduced pipe portion.    
   
   
       34 . The expansion device according to  claim 33 , wherein the valve-opening pressure-receiving surface is formed also by an upstream end face of the reduced pipe portion, and a cross-sectional shape of the reduced pipe portion is configured such that a pressure-receiving area of an entirety of the valve-opening pressure-receiving surface becomes larger than a pressure-receiving area of an entirety of the valve-closing pressure-receiving surface.  
   
   
       35 . The expansion device according to  claim 33 , wherein the restriction mechanism comprises a restriction flow passage formed by a gap between an inner peripheral end edge of the reduced pipe portion and an outer peripheral surface of the shaft-like member, and 
 wherein a passage cross-section of the restriction flow passage is changed in an increasing direction, when the valve element operates in a valve-opening direction.    
   
   
       36 . The expansion device: according to  claim 35 , wherein an upstream end of the shaft-like member is formed with a tapered portion a cross-section of which increases upstream, and the restriction flow passage is formed between a tapered surface of the tapered portion and an inner peripheral end edge of the reduced pipe portion.  
   
   
       37 . The expansion device according to  claim 36 , comprising an engaging member that is supported within the cylinder, and has the shaft-like member engaged at a downstream end thereof; and 
 an adjusting mechanism that adjusts a position of the engaging member within the cylinder, and    wherein a passage cross-section of the restriction passage in a closed state of the valve element can be adjusted by adjusting a position of the shaft-like member by moving forward or backward the engaging member using the adjusting mechanism.    
   
   
       38 . The expansion device according to  claim 32 , wherein the cylinder has a small pipe portion, and a large pipe portion, formed therein in an upstream-to-downstream order, by expanding an inside thereof toward the downstream side, and 
 wherein the valve seat is supported within the large pipe portion, and    wherein the valve element is formed with the valve portion in the form of a hollow cylinder at a location downstream of the body, and has a reduced pipe portion extended upstream of the body such that the reduced pipe portion is movably inserted into the small pipe portion, and    wherein the restriction mechanism is formed by a gap between the reduced pipe portion of the valve element and the small pipe portion of the cylinder.    
   
   
       39 . The expansion device according to  claim 38 , wherein the valve-closing pressure-receiving surface is formed by an upstream end face of the reduced pipe portion, and the valve-closing pressure-receiving surface having a pressure-receiving area larger than a pressure-receiving area of the valve-closing pressure-receiving surface is formed by a downstream facing surface of a stepped portion formed inside the body by the reduced pipe portion.  
   
   
       40 . The expansion device according to  claim 39 , wherein a downstream facing surface having a cross-section larger than a cross-section of the valve portion is formed on a downstream side of the valve portion of the valve element, in a manner continuous therewith.  
   
   
       41 . The expansion device according to  claim 32 , wherein the cylinder has a small pipe portion, and a large pipe portion, formed therein in an upstream-to-downstream order, by expanding an inside thereof in a upstream-to-downstream direction, and 
 the expansion device including a guide pipe in the form of a bottomed hollow cylinder formed such that the guide pipe extends downstream from a downstream opening portion of the small pipe, with a downstream end thereof closed, and a communication hole formed through a side wall thereof in the vicinity of the downstream end, for communicating between an inside and an outside of the guide pipe, the guide pipe having the valve element slidably fitted thereon, and    wherein the valve element has, on an upstream side thereof, a guided portion that is slidable along an outer peripheral surface of the guide pipe, and has a forward end face which can be engaged at a downstream facing surface of a stepped portion provided at a boundary between the small pipe portion and the large pipe portion, and the valve element is formed with a reduced pipe portion at a downstream end thereof, thereby defining a space portion for communicating with the communication hole, between the reduced pipe portion and the guided portion, and    wherein in the space portion, the valve-closing pressure-receiving surface is formed by a downstream facing surface of the guided portion, and the valve-opening pressure-receiving surface larger in pressure-receiving area than the valve-closing pressure-receiving surface is formed by an upstream end face of the reduced pipe portion, and    wherein when the valve element is close to the valve seat, a gap between the reduced pipe portion of the valve element and the guide pipe forms a restriction passage as the restriction mechanism, and    wherein the relief mechanism expands an opening area of the gap between the reduced pipe portion and the guide pipe against an urging force of the elastic member, to thereby allow the refrigerant flowing in from the upstream side to escape downstream at a larger flow rate.    
   
   
       42 . The expansion device according to  claim 41 , wherein a downstream end of the guide pipe is formed with a tapered portion a cross-section of which decreases downstream, and the restriction flow passage is formed between a tapered surface of the tapered portion and an inner peripheral end edge of the reduced pipe portion.