You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to downhole mechanical devices. More particularly a protective sleeve is provided for use on a tubular passing through an installed device, such as a downhole safety valve, to prevent damage to the installed device by the tubular when well operations are performed below the installed device. Also, the protective sleeve is provided for pressure protection of critical components within an installed device and for preventing potentially damaging fluids from making contact with critical components and seals within an installed device, such as a downhole safety valve. 
         [0003]    2. Description of Related Arts 
         [0004]    A variety of equipment is commonly installed in tubing strings in wells. One common type of equipment is a downhole safety valve. Other types include sliding sleeves that can be shifted to open or close conduits to allow fluid to enter or exit the tubing. It is common in well operations to pass smaller tubing, which may be coiled tubing, through the well tubing and through the installed equipment. The smaller tubing, which may be a work string, may be used for conveying fluid into or out of the well or for other well operations. 
         [0005]    The smaller tubing slides through downhole equipment in the tubing, but in some cases it has been found that the smaller tubing may cause damage to the downhole equipment. Damage to a downhole safety valve, for example, can create hazardous conditions or can cause very expensive repair operations. There is a clear need for method and apparatus to protect installed downhole equipment from effects of passage of tubulars through the equipment. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    A protective sleeve that is deployed on the bottom of tubing and is retained in a downhole installed device having a matching locking mechanism is provided. The sleeve may be retained at the selected position in the downhole equipment by shearing of pins between the sleeve and a mandrel. The sleeve may then be retrieved by withdrawing the tubing through the device. The sleeve may include an over pressure balancing mechanism which is operable at any time and a pressure equalization feature which is actuated during recovery. The sleeve protects installed devices from potentially high pressures during fracturing. It also isolates the installed devices from acids and other damaging fluids within the well. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
           [0008]      FIG. 1  is a cross-sectional view of a first embodiment of the invention 
           [0009]      FIG. 1A  is a detailed blow up view of the indicated portion of  FIG. 1 . 
           [0010]      FIG. 1B  is a detailed blow-up view of the indicated portion of  FIG. 1 . 
           [0011]      FIG. 1C  is a detailed blow-up view of the indicated portion of  FIG. 1 . 
           [0012]      FIG. 2  is a cross-sectional view of a setting tool and the protective sleeve in the pre-set position within a safety valve. 
           [0013]      FIG. 3  is a cross-sectional view of a running tool and sleeve positioned within a safety valve in the set position. 
           [0014]      FIG. 4  is a cross-sectional view of the running tool and sleeve after jarring up to release the running tool. 
           [0015]      FIG. 5  is a cross-sectional view of a pulling tool positioned within the sleeve. 
           [0016]      FIG. 6  is a cross-sectional view of the pulling tool at set down full weight. 
           [0017]      FIG. 7  is a cross-sectional view showing the pulling tool collet engaging the internal profile of the sleeve collet. 
           [0018]      FIG. 8  is a cross-sectional view of the pulling tool as it initially is pulled to engage the sleeve. 
           [0019]      FIG. 9  is a cross-sectional view of the pulling tool after being jarred up to shear the sleeve release pins. 
           [0020]      FIG. 10  is a cross-sectional view of the pulling tool after being jarred up further to shear the equalizing dart. 
           [0021]      FIG. 11  is a cross-sectional view of the pulling tool pulling the protective sleeve out of the safety valve. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    Referring to  FIGS. 1-11  an embodiment of a protective sleeve according to the invention is disclosed. The protection sleeve  51  includes a locking collet housing portion  67  in which locking collet  54  is slidably mounted. Collet housing  67  is attached to a downstream housing  64  which serves as a protective sleeve for the installed device, and includes a plurality of seals  65  on an outer surface  142  of its lower portion. Collet housing  67  and main housing  64  are cylindrical in shape and are tubular so as to provide an interior passageway for either fluids or other tubular equipment. 
         [0023]    Locking collet  54  includes a plurality of slots  55  that form finger like portions  45 . A plurality of radically spaced ridges  49  as shown in  FIG. 1A  are formed on the outer surface of fingers  45  to form a collet in a manner known in the art. 
         [0024]    Locking collet  54  also includes a profile annular groove  104  on an inside surface as shown in  FIG. 1 . Locking collet further includes an annular ridge or raised portion  46  on its outer surface, and an axially extending slot  47  on its other surface as shown in  FIG. 1B . 
         [0025]    Locking collet housing  67  includes a plurality of interior annual groves  57 ,  58 , and  59  as best shown in  FIG. 1A  and a plurality of annular seals  56  on a raised surface  61 . A plurality of locking dogs  53  are positioned within openings provided in the locking collet housing and engage collet  54  at a first, non-locking position shown in  FIG. 1 . 
         [0026]    Locking dogs  53  are adapted to be moved in a radial direction into a groove  81  on the interior surface of the safety valve  80  as best shown in  FIGS. 8 and 9 . 
         [0027]    Locking collet housing  67  also includes a frangible pressure equalizing dart  70  having a frangible portion  71  that is positioned within slot  47  of the locking collet as shown in  FIG. 1B . Dart  70  also includes a flow passage  52 . A no-go shoulder  77  is formed on the outer surface of locking collet housing  67  and prevents further downhole movement of the protective sleeve within safety valve housing  80 . 
         [0028]    As shown in  FIG. 1C , downstream housing  64  includes a pressure balancing chamber  73  in which a floating piston  75  is positioned. A shear pin  74  engages a groove  91  in piston  75  and initially prevents movement of the piston within chamber  73 . 
         [0029]    As shown in  FIG. 2 , a running tool  100  including a body portion  111  and a top portion  103  is utilized to set the protective sleeve  51  within safety valve housing  80 . The running tool  100  is a Z running tool, known in the industry but slightly modified. Running tool  100  includes a first shear pin  101  and a second shear pin  102  as shown in  FIG. 2 . 
         [0030]    As the running tool is moved downhole as shown in  FIG. 3  pins  102  are sheared and, locking dogs  53  are moved radically outwardly by shoulder  46  into groove  81  and retrieval shear screws  105  are engaged in a groove  41  on the outside surface of locking collet  54 . The protection sleeve is now locked within safety valve housing  80 , with ridges  49  now positioned within groove  59  of locking sleeve housing  67 . 
         [0031]    As running tool  100  is removed from the locking collet as shown in  FIG. 4 , shear pin  101  is sheared thereby releasing the running tool  100  from housing  67 . 
         [0032]    In order to remove the sleeve from the safety valve housing, a pulling tool  120  is run to the set depth as shown in  FIG. 5  with flange  122  of the pulling tool positioned as shown adjacent groove  104  in the locking collet. As the running tool is set down as shown in  FIG. 6  flange  122  is positioned within groove  104  of the locking collet  59 . 
         [0033]    As the running tool is set down at full weigh shown in  FIG. 7 , collet fingers  140  of the pulling tool are positioned within groove  104  of the locking sleeve. 
         [0034]    To remove the protective sleeve, the pulling tool  120  is pulled upward so that flange  122  moves into contact with collet finger  140  of the pulling tool. The pulling tool is jarred upwardly so that retrieval shear screws  105  are sheared and locking collet  54  moves upwardly to the position shown in  FIG. 9 , thereby allowing dogs  53  to move radially inwardly out of grove  81 . Ridges  49  of the locking collet  54  are now engaged in groove  58 . 
         [0035]    The pulling tool is next jarred upwardly again to the position showing  FIG. 10 . This will sever equalizing dart  70  thereby equalizing the pressure on the inside and outside of the main housing of the protective sleeve. At this point, the pulling tool can be pulled in an upward direction to remove the protective sleeve from the safety valve housing as shown in  FIG. 11 . Ridges  49  of locking collet  54  are now positioned within grove  57 . 
         [0036]    Should the pressure differential between the inside and outside of the protective sleeve become too great at any time, shear pin  74  will fail and piston  75  can float within chamber  73  thereby balancing the pressure via port  76 . 
         [0037]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Summary:
A protective sleeve is deployable within an oil/gas well to protect a device installed in the well such as a safety valve, for example. The sleeve includes a pressure equalizing dart and an overpressure protection piston. The sleeve also serves to isolate an installed device from harmful substances such as acids and other corrosive fluids.