Abstract:
In combination, a liquid sample pump and an integral self-cleaning filter element will elongate the maintenance interval for the pump which saves on time and labor costs. The filter element itself is small, economical to make and forms an integral part of the liquid sample pump. A flow passageway continuously directs turbulent liquid to the underside of the filter element to sweep debris from the filter element and return such debris to the pipeline. When it is necessary to service the liquid sample pump, it is quick and easy to remove and replace the filter element, which also saves on time and labor costs. A bleed valve assembly allows air to be bled from the sample pump prior to operation, enhancing seal life. An optional muffler assembly excludes insects from the inside of the sample pump, again elongating maintenance intervals. An optional return valve assembly allows unused sample to be returned to the pipeline, thus benefitting the environment. The filter element may be formed from a metal screen or a sintered metal disk.

Description:
DISCUSSION OF THE PRIOR ART 
     Samplers are known, such as the Light Liquid Sampler produced by YZ Systems, Inc. of 3101 Pollok Dr., Conroe, Tex. 77303. See, for example the YZ System Support Manual for the PNR-2s-1.5, 3,5P-0A. Some prior art liquid products have filter elements that get clogged by debris entrained in the liquid. Some prior art liquid samplers have dead space in the sample mechanism. Some prior art products do not have a continuously flowing loop of liquid passing through the sampler. The present invention has a loop of liquid continuously flowing through the sampler, has minimal dead space and an integral self-cleaning filter element. A continuously flowing loop of liquid through the sampler is sometimes called a “hot loop” in the industry. 
     Collins Products Company of Livingston, Tex., sells the prior art Swirlklean™ filter as shown in the 2011 Catalog on page 3. The Swirlklean filter element is a heavy, expensive, stand-alone filter element often used in refineries that costs from about $360 to about $900 or more. The Swirlklean filter is sometimes installed upstream of and separate from a sample pump. This filter element uses a bypass stream that enters the housing tangentially to a drum-like filter element; the circular current around the filter element is intended to keep debris washed off the drum-like filter element. The Swirlklean filter uses a continuously flowing stream, but it has a different structure. The Swirlklean filter is not integral with a sample pump, like the present invention. The cost of a Swirlklean filter and prior art sample pump together are more expensive than the present invention and more difficult to install and maintain. Collins Products Company is believed to own at least the following patents on self-cleaning filter systems: U.S. Pat. Nos. 4,533,471; 3,598,238; 4,533,471 and 4,693,815 
     A search located the following patents owned by PGI International of Houston, Tex.: U.S. Pat. Nos. 5,522,708; 5,191,801 and 5,092,742. The &#39;742 Patent provides a strainer between the process line and the sampling pump to prevent debris from entering the pump. However, the strainer does not extend across the entire cross-section of the hot loop path, so all fluid continually flowing through the hot loop and returning to the process line is not cleaned. A purge line within the manifold has its inlet closely adjacent the strainer to automatically clean the strainer during conventional purging of the sample vessel. The present invention has continuous cleaning of the filter element caused by the continuously flowing loop; unlike the &#39;742 Patent which only cleans the strainer during periodic purging of the sample vessel. The continuous cleaning of the present invention is better than periodic cleaning. 
     The search also located the following patents: U.S. Pat. Nos. 2,726,548; 6,400,575; 4,727,758; 5,423,228; 5,641,894; 5,736,654; 7,540,206; 6,076,410; 8,056,400. Many of these patents use periodic back flush techniques similar to swimming pool filter elements. The continuous cleaning of the present invention is better than periodic back flushing techniques. 
     Welker, Inc., formerly known as Welker Engineering Company of Sugar Land, Tex., the assignee of the present invention, owns several relevant patents as follows: U.S. Pat. Nos. 6,338,359; 6,761,757; and 6,764,536 (hereinafter &#39;536 Patent). The &#39;536 Patent discloses an apparatus that functions on a multiphase fluid that includes both gas and liquids. The present invention functions only on liquids, not multiphase fluids. Natural gas, even though generally referred to as a gas, when transported, often contains liquid and gas hydrocarbon components. The “liquid eliminator” of the &#39;536 Patent is intended to separate the liquid component from the gaseous component in a natural gas stream because many instruments will not accept the liquid component and still function properly, such as a gas chromatograph. The porous membrane  41 , described in the &#39;536 Patent, forms gas flow channels to allow gas to pass through the membrane. These flow channels are so small that they exclude all liquids. The present invention functions only on liquids. Therefore, the filter element of the present invention cannot be substituted for the filter element in the &#39;536 Patent, and the filter element disclosed in the &#39;536 Patent cannot be used in lieu of the filter element in the present invention. 
     The porous membrane described in the &#39;536 Patent is supported by an insert which obstructs the center portion of the porous membrane from contact with the inlet stream. Therefore, a substantial portion of the filter element is not in contact with the inlet stream because of the insert. Therefore, the inlet stream is incapable of sweeping debris from a substantial portion of the porous membrane. Without the insert, the flimsy porous membrane may fail. 
     SUMMARY OF THE PRESENT INVENTION 
     Separate filters are sometimes placed upstream of prior art sample pumps to prevent debris entrained in the liquid from entering the pump. Separate upstream filters may be heavy, expensive, and in combination with a sample pump, are more difficult to install and maintain. The present invention utilizes a small, light-weight, integral filter element in the sample pump. The small, light-weight, integral filter element is often less expensive than separate upstream filters. The threaded version of the present invention weighs about 16 U.S. pounds and retails for approximately $4,300. The threaded version of the present invention is easy to install because it simply screws into a thread-o-let in the pipeline. 
     The flanged version of the present invention weighs about 26 U.S. pounds and retails for approximately $4,900. The flanged version connects to a mating flange on the pipeline with a plurality of nuts and bolts, as is well known in the industry. The flanged version is also easy and quick to install. The sintered metal filter element retails for about $15 and the metal mesh filter element retails for about $5. 
     Liquids flowing through a pipeline need to be sampled for various reasons. In the present invention, a loop of liquid continuously flows through a passageway in the sample pump and returns to the pipeline, assuring that fresh sample is taken when the sample pump strokes, or takes a sample. In such continuously flowing loops of liquid, debris may clog the filter element, especially in a sample pump. A clogged filter element requires unwanted disassembly of the sample pump, removal and replacement of the filter element and reassembly of the sample pump, which is time consuming, expensive and stops the sample process during the unwanted maintenance. 
     In the present sample pump, the liquid flowing through the continuous loop is turbulent, not laminar. This liquid passes from the pipeline, up into the pitot probe, makes a 90° turn and passes through a horizontal inlet passageway, past the open inlet on/off valve, through an angled inlet passageway to an agitation chamber below the filter element, through an angled outlet passageway, past the open outlet on/off valve, through a horizontal outlet passageway, makes a 90° turn, passes through an outlet passageway and is discharged back into the pipeline. Because of the twists and turns of the tortuous passageway through the present sample pump, the liquid becomes turbulent, and when it reaches the agitation chamber, it sweeps debris from the bottom surface of the filter element and back into the pipeline. The turbulent liquid in the agitation chamber self-cleans the filter element. The exact shape of the flow passageway is not critical; the fact that the liquid becomes turbulent as it passes through the tortuous passageway and is turbulent below the filter element is necessary for the self-cleaning action. 
     Even with a self-cleaning filter, it will eventually be necessary to replace the filter element of the present invention; when maintenance is necessary, the integral self-cleaning filter is quick and easy to service. Two on/off valves are closed, which stops the flow of liquid through the hot loop; four nuts are removed from the lower part of the pump, allowing fast and easy disassembly of the sample pump and quick replacement of the filter element. If warranted, the seal assembly on the lower portion of the piston rod may also be replaced. 
     The cartridge type check valves on this sample pump are also easy to maintain and may be checked using air pressure. Several different types of replaceable filter elements may be used in this sample pump, including a sintered metal filter element or a metal mesh filter element. The sintered metal filter element may be used with natural gas liquids such as ethane, propane, butane, etc. The metal mesh filter element may be used with light crude oil or condensate separated from natural gas. A bleed valve may be provided to drain air from the variable volume sample chamber; further, when air is bled from the variable volume sample chamber, liquid fills the chamber and acts as a lubricant to prolong the life of the seal assembly on the lower portion of the elongate piston rod. An optional return valve allows unused sample to be returned to the pipeline, thus benefitting the environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of the sample pump with integral self-cleaning filter positioned in a pipeline. A sintered metal filter element is shown in  FIG. 1 . For illustrative purposes, the internal structure of the sample pump has been rotated 90° in this view relative to the pitot probe, to better understand the apparatus. 
         FIG. 2  is a section view of the sample pump with integral self-cleaning filter element. A sintered metal filter element is shown in  FIG. 2 . 
         FIG. 3  is a section view of the sample pump with integral self-cleaning filter similar to  FIG. 1 , except the power piston is moving upward, as indicated by the arrows, to allow a sample to be drawn into the variable volume sample chamber. A sintered metal filter element is shown in this figure. 
         FIG. 4  is an enlargement of the inlet cartridge check valve assembly in the open position. 
         FIG. 5  is a section view of the sample pump with integral self-cleaning filter similar to  FIG. 1 , except the power piston is moving downward, as indicated by the arrows, to pump sample into the sample container. 
         FIG. 6  is an enlargement of the outlet cartridge check valve assembly in the open position. 
         FIG. 7  is an enlargement of the sealing assembly on the end of the piston rod. 
         FIG. 8  is an enlargement of the inlet check valve assembly in the closed position with a sintered metal filter element. The turbulent liquid is indicated by the swirling lines. 
         FIG. 9  is a section view along the line  9 - 9  of  FIG. 8 . The turbulent liquid is indicated by the swirling lines. 
         FIG. 10  is an enlargement of the inlet check valve assembly in the open position with a metal screen filter element. 
         FIG. 11  is a view along the line  11 - 11  of  FIG. 2 . 
         FIG. 12  is a view along the line  12 - 12  of  FIG. 2 . 
         FIG. 13  is a view along the line  13 - 13  of  FIG. 2 . 
         FIG. 14  is a section view of the inlet on/off valve in the open position. 
         FIG. 15  is a section view of the sample pump with integral self-cleaning filter element and related equipment shown by block diagram. This version of the invention threads into a thread-o-let welded to the pipeline. This is an accurate view of the apparatus, unlike some of the prior figures that were for illustrative purposes. 
         FIG. 16  is a section view of the sample pump with integral self-cleaning filter element. This version of the invention has a flange to connect to a mating flange on the pipeline using nuts and bolts. This is also an accurate view of the invention, unlike some of the prior figures that were for illustrative purposes. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The word “up” as used herein means away from the pipeline  70  and the word “down” as used herein means toward the pipeline  70 . Referring to  FIGS. 1 and 2 , the sample pump with integral self-cleaning filter element is generally identified by the numeral  20 . Solely for illustrative purposes, the structure of the sample pump in  FIG. 1  has been rotated 90° counter-clockwise relative to the pitot probe, when viewed from above.  FIG. 2  has been rotated clockwise relative to the pitot probe, when viewed from above, to better illustrate the tie rods  38  and  118 . 
     A means for stroking a power piston up and down includes the power piston  22  slideably located in an upper cylinder  24 , which divides the upper cylinder into an upper chamber  26  and a lower chamber  28 , better seen in subsequent figures. The upper chamber  26  is in fluid communication with the upper in/out port  30  and the lower chamber  28  is in fluid communication with the lower in/out port  32 . 
     Referring back to  FIG. 1 , an upper end cap  34  seals against the upper cylinder  24  by the o-ring  42 ; a body  36  seals against the upper cylinder  24  by the o-ring  44 . The upper end cap  34 , the upper cylinder  24  and the body  36  are held together by a plurality of tie rods  38 , better seen in  FIG. 2 , secured by a plurality of nuts  40 . The power piston  22  seals against the inside circumference of the upper cylinder  24  by an upper PolyPak® seal assembly  46  and a lower PolyPak® seal assembly  48 . The PolyPak® seal assembly  46  and  48 , model number 1250-0250 may be formed from Viton® polymer and are available from Parker whose headquarters is in Salt Lake City, Utah. 
     A means for adjusting the volume of the variable volume sample chamber  68 , better seen in subsequent figures, includes the following: a vertical measurement bar  52  secured to the upper end cap  34 , a knob  54  permanently secured to a threaded shaft  56  which threadably engages a nut  58  permanently secured to the upper end cap  34 , and a piston stop  60  secured to the threaded shaft by a set screw  62 . The upper end cap  34  is removably connected to the body  36 . Volumetric measurement indicia  64  may be inscribed on the vertical measurement bar  52  such as: 0 cc, lee, 2 cc, 3 cc, 4 cc, 5 cc, 6 cc, 7 cc and 8 cc. The sample volume range may vary depending on the application. A measurement line  66  is inscribed on the knob  54 . The knob is rotated up or down until the measurement line  66  aligns with the selected volumetric measurement indicia  64 . The piston stop  60  then prevents the power piston  22  from rising any further than desired, thus defining the volume of sample drawn into the variable volume sample chamber  68 , better seen in subsequent figures. 
     An elongate piston rod  100  is secured to the power piston  22  so the elongate piston rod moves up and down with the travel of the power piston  22 . A lower cylinder  102  surrounds a portion of the elongate piston rod  100 . The lower cylinder  102  defines an inside circumferential surface  103 , best seen in  FIG. 7 . A bore  104  is formed in the body  36  and is sized and arranged to receive one end of the lower cylinder  102 . A bore  106  is formed in the housing  108  and is sized and arranged to receive a portion of the other end of the lower cylinder  102 . One end of the lower cylinder  102  is sealed against the body  36  by the upper o-ring  110 ; the other end of the lower cylinder  102  is sealed against the housing by the lower o-ring  112 . A central bore  114  is formed in the center of the lower cylinder and is sized and arranged to receive a portion of the elongate piston rod  100 . 
     Referring now to  FIG. 2 , a plurality of tie rods  118 , pass through elongate bores  120  in the lower end cap  116  and the housing  108  to thread into threaded apertures  122  in the body  36 . A plurality of nuts  124  threadably engage the exposed threaded ends of the tie rods  118  to secure the body  36  to the lower cylinder  102  to the housing  108  and to the lower end cap  116 . Removal of the nuts  124  allows quick and easy disassembly of the lower section of the liquid sample pump  20 , if it is necessary to service the apparatus. The lower end cap  116  defines a neck  126  which threadably engages a thread-o-let  128  welded to the pipeline  70 . Wrench flats  82  are formed above the neck  126 . As indicated by the flow arrow, liquid is flowing through the pipeline  70 . 
     A continuous liquid flow passageway is generally identified by the numeral  152  and is also known as a “hot loop” in the industry. The straight flow arrows in  FIGS. 1, 3 and 5  show the direction of flow through the continuous liquid flow passageway  152 ; however, the flow itself becomes turbulent as it passes through the tortuous passageway of the hot loop. The inlet  151  for this continuous liquid flow passageway  152  is a pitot tube  154  and the outlet  155  is a shorter tube  174  located downstream of the inlet. The inlet and the outlet for the continuous liquid flow passageway are both in fluid communication with the liquid flowing through the pipeline  70 . The inlet and the outlet should be formed in the neck  126  of the present apparatus to facilitate installation and removal of the liquid sample pump  20  on the pipeline. 
     Referring back to  FIG. 1 , the liquid enters the pitot tube  154 , travels through an up tube  96 , makes a 90° turn and passes through a horizontal inlet passageway  84 , past the inlet on/off valve assembly  156 , through an angled inlet passageway  86  to an agitation chamber  88  below the self-cleaning filter element  160 , through an angled outlet passageway  90 , past the outlet on/off valve assembly  172 , through a horizontal outlet passageway  92 , makes a 90° turn, passes through a down tube  94  and is discharged back into the pipeline by the shorter tube  174 . Because of the twists and turns of the tortuous passageway through the present liquid sample pump  20 , the liquid becomes turbulent and when it reaches the agitation chamber, it sweeps debris from the bottom surface of the self-cleaning filter element  160 , better seen in  FIG. 2  and subsequent figures, and back into the pipeline  70 . The turbulent liquid in the agitation chamber  88  self-cleans the filter element  160 . The shape of the flow passageway is not critical; the fact that the liquid becomes turbulent before it passes below the filter element  160  in the agitation chamber  88  is necessary for the self-cleaning action. 
     Referring now to  FIGS. 3 and 4 , the liquid sample pump with integral self-cleaning filter element  20  is actuated to stroke up and draw sample from the pipeline  70  into the variable volume sample chamber  68  as indicated by the flow arrows. Referring now to  FIG. 16 , the upper in/out port  30  is connected by tubing  72  to a pneumatic/electric solenoid  74  which connects to a source  76  of pressurized air. The lower in/out port  32  is connected by tubing  78  to the pneumatic/electric solenoid  74 . A control system  80 , which can include an electronic flow measurement computer and/or a programmable logic controller and/or a distributed control system, is wired to the pneumatic/electric solenoid  74 . When the control system  80  actuates the pneumatic/electric solenoid  74 , pressurized air flows through the tubing  78  into the lower chamber  28 , as best seen in  FIG. 3 , driving the power piston  22  up which expels air from the upper chamber  26 , through the tubing  72  back to the pneumatic/electric solenoid  74 . As the power piston  22  strokes up, it carries the elongate piston rod  100  up, as shown by the arrow, drawing liquid from the agitation chamber  88  through the self-cleaning filter element  160  past an inlet check valve assembly  190 , which is shown in the open position in  FIGS. 3 and 4 . In  FIG. 3 , the outlet check valve assembly  192  is in the closed position. The power piston  22  moves up in the upper cylinder  24  until it hits the piston stop  60 . 
     To reverse the direction of the power piston  22  as seen in  FIG. 5 , the control system  80  actuates the pneumatic/electric solenoid  74  in the opposite direction and pressurized air from the source  76  flows through the tubing  72  into the upper chamber  26  driving the power piston  22  down and air in the lower chamber  28  exits through the tubing  78  back to the pneumatic/electric solenoid  74 . In this fashion, the power piston  22  is stroked down. Liquid passes from the variable volume sample chamber  68  through the sample outlet  194  as indicated by the arrows and past the outlet check valve assembly  192  to the sample container  196 , as best seen in  FIG. 16 . In this manner the elongate piston rod  100  strokes down and bottoms in the variable volume sample chamber  68  as shown in  FIG. 1 . 
     To summarize, the elongate piston rod  100  begins a cycle at the bottom of the variable volume sample chamber  68 , as better seen in  FIG. 2 . The elongate piston rod  100  then strokes up, as shown by the arrows in  FIG. 3  until the power piston  22  hits the piston stop  60 . Liquid is drawn into the variable volume sample chamber  68  during the up stroke of the elongate piston rod  100 , as shown in  FIG. 3 . The elongate piston rod  100  then strokes down, as shown by the arrows in  FIG. 5 , until it bottoms in the variable volume sample chamber  68 . Liquid is pumped from the variable volume sample chamber  68  into the sample container  196 . The elongate piston rod  100  comes to rest at the bottom of the variable volume sample chamber  68 , as better seen in  FIG. 2 . The liquid sample pump  20  is then ready to begin another stroke cycle. 
     Referring now to  FIG. 7 , a portion of the body  36  is shown at the top of the drawing and a portion of the housing  108  is shown at the bottom of the drawing. A lower o-ring  112  seals the housing  108  against the lower end of the lower cylinder  102 . The lower cylinder defines an inside circumferential surface  103 . Referring to the end of the elongate piston rod  100 , a seal means includes a first wiper  204  and a second wiper  206  surround o-ring  208 ; at the end of the elongate piston rod  100  is a PolyPak seal assembly  210 . This seal means engages the inside circumferential surface  103 . The end  214  of the elongate piston rod  100  is touching the bottom  212  of the variable volume sample chamber  68 , as better seen in  FIGS. 3 and 5 . 
     Referring now to  FIG. 8 , the inlet check valve assembly  190  is shown in enlarged format in the closed position. A metallic washer  232  with a central opening  233  sits on the upper surface  162  of the sintered metallic filter element  166  to hold the filter element in place. An 
     o-ring  234  seals the metallic washer  232  against the lower end cap  116 . Another o-ring  236  is positioned in a channel  237  formed in the lower side of the metallic washer  232  and seals against the sintered metallic filter element  166  and the metallic washer  232 . As best seen in  FIG. 8 , the turbulent liquid flowing through the agitation chamber  88  of the continuous liquid flow passageway  152  sweeps against the lower surface  164  of the sintered metallic filter element  166  to remove debris from the lower surface  164 . 
     A self-cleaning filter element  160  may be a sintered metal disk-shaped filter element  166  which is an off-the-shelf item from MOTT Corporation in Farmington, Conn.; the website is www.mottcorp.com. The sintered metallic filter element  166  may be about 0.625 inches in diameter and about 0.125 inches thick. MOTT calls this self-cleaning filter element a “porous metal media”, 40 micron grade and may sometimes be referred to in the industry as a “sintered stone” filter element. Filter elements with 20, 60 or 100 micron grade may also be suitable in this invention, depending on the location, application and the amount of debris in the pipeline. 
     The self-cleaning filter element  160  may, in the alternative, be formed from a disk-shaped metal mesh screen  168 , as better seen in  FIG. 10 . The metal mesh is available from CPI Wire Cloth &amp; Screen, Inc. located in Pearland, Tex.; the website is www.cpiwirecloth.com. The disk-shaped screen is about ⅝ inch in diameter, about 0.01135 inches thick and formed from 304 stainless steel. The metal screen is about 35 mesh, which is about 500 microns. In other words, anything smaller than 500 microns will pass through this 35 mesh filter element; anything larger than 500 microns will not pass through the metal mesh. The 35 mesh filter element is suitable for non-stabilized crude and/or condensate from the Eagle Ford Shale formation in Texas and perhaps elsewhere. A larger or smaller sized screen may be suitable for use in this invention depending on the location, application and degree of debris in the pipeline. Both of the filter elements  166  and  168  are disk-shaped having an upper surface  162  and a lower surface  164 , better seen in  FIGS. 8 and 10 . 
     The inlet check valve assembly  190  is in the closed position in  FIG. 8  and in the open position in  FIG. 10 . The inlet check valve assembly  190  includes an o-ring  240  which seals the inlet check valve assembly  190  against the housing  108 . The inlet check valve assembly  190  further includes a movable cartridge valve  242 , a metal seal  244  and a spring  246  which urges the movable cartridge valve  242  into the closed position as shown in  FIG. 8 . The inlet check valve assembly  190  is an off the shelf cartridge check valve model number 2203D-18-10 available from Kepner Products Company located in Villa Park, Ill.; the website is www.kepner.com. The outlet check valve assembly  192  is the same product from Kepner Products Company. 
       FIG. 9  is a section view along the line  9 - 9  of  FIG. 8 . The swirled lines indicate the turbulent liquid flow through the angled inlet passageway  86  and the agitation chamber  88  to the angled outlet passageway  90 . 
       FIG. 10  is similar to  FIG. 8 , except the inlet check valve assembly  190  is in the open position and the liquid sample is flowing from the agitation chamber  88  of the continuous liquid flow passageway  152  through the central opening  233  in the metallic washer  232 , through apertures  250  of the movable cartridge valve  242  of the inlet check valve assembly  190  and out the sample outlet  194  to the sample container  196 , best seen in  FIG. 12 . 
       FIG. 11  is a section view along the line  11 - 11  of  FIG. 2 . A muffler assembly  252  threadably engages a muffler port  254 . The muffler assembly  252  is an off-the-shelf item, model number 4450K1, produced by McMaster Carr in Atlanta, Ga.; website www.mcmaster.com. The muffler port  254  connects to a passageway  256  which connect to the annulus  258  formed between the outside circumference of the elongate piston rod  100  and the inside circumference  260  of the lower cylinder  102 . The muffler assembly  252  allows air to escape to atmosphere from the annulus  258  as the elongate piston rod  100  strokes up and allows air to be drawn into the annulus  258  as the elongate piston rod  100  strokes down. The muffler assembly  252  also prevents insects from entering the annulus  258  and building obstructive homes in the liquid sample pump with integral self-cleaning filter  20 . 
       FIG. 12  is a section view along the line  12 - 12  of  FIG. 2 . A bleed valve assembly is generally identified by the numeral  270 ; the bleed valve assembly  270  threadably engages a bleed valve port  272  which is in fluid communication with a passageway  274  which is in fluid communication with the sample passage  276 . The purpose of the bleed valve assembly  270  is to bleed air out of the sample passage  276  and the other passageways that conduct the liquid sample, including the continuous liquid flow passageway  152 . The liquid sample pump  20  does not work well until all of the air is bled from the liquid sample pump  20 . To bleed the air, the hex nut  273  on the end of the bleed valve is turned and air exits the air outlet  271  to atmosphere as indicated by the flow arrow. The bleed valve assembly  270  is an off-the-shelf item, model no. SS-BVM2, ⅛ inch NPT from Swagelok; the headquarters are located in Solon, Ohio, and distribution is throughout the U.S. The website is www.swagelok.com. 
       FIG. 13  is a section view along the line  13 - 13  of  FIG. 2 . The inlet on/off valve assembly  156  is shown in the 12 o&#39;clock position, and the outlet on/off valve assembly  172  is shown in the six o&#39;clock position. A third valve assembly  176  is shown in the three o&#39;clock position in the drawing. The third valve may be used to return any unwanted sample to the pipeline  70 . Sample is typically collected in a pre-pressurized cylinder. The pre-pressurized cylinder allows unused sample to be returned against pipeline pressure through the third valve assembly  176 . 
       FIG. 14  is an enlargement of the outlet on/off valve assembly  172  and identical to the inlet on/off valve assembly  156 . These on/off valve assemblies are normally in the open position, as shown in this figure, so the liquid can flow through the hot loop. These valve assemblies are shifted to the closed position only to maintain the liquid sample pump  20 . 
       FIG. 15  is a block diagram showing a true side view of the liquid sample pump with integral self-cleaning filter  20  and associated equipment. This view of the liquid sample pump  20  has not been altered for illustrative purposes. This version of the liquid sample pump  20  has a threaded neck which threads into a thread-o-let in the pipeline  70 . The outlet check valve assembly  192  is typically connected either directly to a sample container  196  or indirectly connected by tubing to the sample container  196 . This perspective view shows how the apparatus is held together by the tie rods  38  and the nuts  40 , tie rods  118  and the nuts  124 . When it is necessary to replace the filter element  160 , an operator turns the hot loop off by closing the inlet on/off valve assembly  156  and outlet on/off valve assembly  172 . The operator then removes the nuts  124  which will allow separation of the housing  108  and the lower end cap  116 . The filter element  160  may then easily be removed and replaced. If necessary, the seals, 
     o-rings and wipers on the end of the elongate piston rod  100  may also be removed and replaced. The sample pump is reassembled and the on/off valve assemblies are opened, which reopens the hot loop. The operator then opens the bleed valve assembly  270  to bleed air from the sample pump, and then closes the bleed valve assembly. The sample pump is then ready to take new samples. 
       FIG. 16  is a true side view of an alternative embodiment of the liquid sample pump with integral self-cleaning filter  20 . This view of the liquid sample pump  20  has not been altered for illustrative purposes. A bottom flange  280  is mounted on the pipeline  70 . An upper flange  282  mates with the bottom flange  280  on the pipeline  70 ; both flanges are held together with nuts  284  and bolts  286 , as is well known to those skilled in the art. A neck  288  is typically welded to the upper flange  282 ; the neck  288  supports the sample pump with integral self-cleaning filter  20 . Some customers prefer flanged connections and some prefer thread-o-let connections; therefore the sample pump with integral self-cleaning filter  20  is offered in two different versions by the assignee.