CN110131454B - Constant-current sampling flow limiting valve - Google Patents
Constant-current sampling flow limiting valve Download PDFInfo
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- CN110131454B CN110131454B CN201910488041.2A CN201910488041A CN110131454B CN 110131454 B CN110131454 B CN 110131454B CN 201910488041 A CN201910488041 A CN 201910488041A CN 110131454 B CN110131454 B CN 110131454B
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16K—VALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
- F16K17/00—Safety valves; Equalising valves, e.g. pressure relief valves
- F16K17/20—Excess-flow valves
- F16K17/22—Excess-flow valves actuated by the difference of pressure between two places in the flow line
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/02—Devices for withdrawing samples
- G01N1/22—Devices for withdrawing samples in the gaseous state
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- Pathology (AREA)
- Sampling And Sample Adjustment (AREA)
Abstract
The invention discloses a constant-current sampling flow-limiting valve, which comprises a flow-limiting hole and a main valve body, wherein the flow-limiting hole is communicated with an air inlet, the main valve body comprises a main cover body and a rear cover, two cavities are arranged in the main cover body, one cavity is a through air channel, one end of the air channel is communicated with the flow-limiting hole, and the other end of the air channel is provided with a sampling tank interface which can be communicated with a sampling tank; the other is a space between the main cover body and the rear cover, an elastic membrane is arranged in the space, the elastic membrane is in sealing contact with the main cover body, and an elastic cavity is reserved between the elastic membrane and the wall of the air passage channel; the rear cover is positioned at the outer side of the elastic membrane and is fixed with the main cover body; a piston type nozzle is arranged in the air passage, and the air passage is partitioned into an air inlet section and an air outlet section by the piston type nozzle; the air inlet section of the air channel is communicated with the elastic cavity, and the elastic cavity is communicated with the air outlet section of the air channel through the piston type nozzle; the back cover is provided with an atmospheric pressure balance port. The invention achieves real constant current limiting through secondary current limiting.
Description
Technical Field
The invention relates to a flow limiting valve for sampling, in particular to a constant-flow sampling flow limiting valve for keeping the sampling flow constant.
Background
Air samples are collected by a sampling tank (Su code tank) which is vacuumized in advance, and two modes of instantaneous samples and average samples exist. The collection of the instantaneous sample is relatively simple, and the sampling tank valve is only required to be opened during operation, and the vacuum in the tank is utilized to suck the air sample into the sampling tank in a short time (usually less than 10 seconds). Samples collected in this manner represent ambient air pollution conditions at the moment the valve is opened. The collection of the average sample (also known as a mixed sample) is somewhat complicated, and when the valve is opened to sample, the flow rate of the gas sample into the sample tank is controlled so that the gas enters the sample tank at the same flow rate (constant velocity) throughout the sampling period. Samples collected in this manner represent an average contamination of the ambient air during the entire sampling process. In ambient air quality monitoring, the average sample is typically taken for half an hour (0.5 h), one hour (1 h), three hours (3 h), eight hours (8 h), one day (24 h) and one week (144 h). The magnitude of the sampling flow depends on the sampling duration, the volume of the sampling tank, the final residual vacuum (pressure), etc. The typical sampling flow rates are shown in table 1. For example, when a sampling tank with a volume of 6 liters is used to collect an average sample for 3 hours and the final pressure is 25inHg (absolute), the target sampling flow rate should be controlled to be about 28.9 mL/min.
Table 1 common target sample flow (mL/min) for tank sampling
Note that: the above flow rates were reference values at one atmosphere (101.325 kPa) and a sampling end pressure of-4 inHg (86.6 tank volume)
Volatile Organic Compounds (VOCs) are important precursors responsible for the pollution of fine particulate matter (PM 2.5) and ozone (O3), and have therefore become an important point of national environmental pollution control in recent years. In the evaluation of the quality of VOCs environmental air, because the concentration of VOCs in the environmental air has large space-time variation, the instantaneous sampling mode is rarely used because of the poor representativeness, and the average sample of 3h,8h or 24h is adopted in the general monitoring project. And the representative of the average sample is based on the stability of the sampled flow during the sampling process, it is important to maintain the accuracy and stability of the sampled flow throughout the sampling process. Therefore, measurement and control of sampling flow is an important element in monitoring the environment of VOCs. A simple and effective method for controlling the actual sampling flow has important significance in ensuring the data quality of the collected average sample, adjusting the sampling flow limiting valve and the like.
In actual sampling, the pressure of the gas in the tank gradually increases (the vacuum degree decreases) and the pressure difference between the gas and the ambient air gradually decreases along with the sampling process, so that the flow rate of the gas sample gradually decreases, if the gas sample is not controlled, the requirement of constant-flow sampling of the average sample cannot be met. In current environmental monitoring, there are three methods for controlling the gas flow rate for average sample collection:
1. orifice-based or orifice-based valves (such as orifice-limiting needle valves) are used to restrict the flow of gas into the canister. The advantage of this method is that it is simple in construction, is a purely mechanical device (without electronic components) and is therefore particularly stable, without the need for power (power supply or battery). The disadvantage is that, limited by the orifice plate principle, the flow is maintained constant only when the pressure drop between the external atmospheric pressure and the pressure in the tank exceeds a critical value. As sampling proceeds, the pressure in the tank gradually increases and the external pressure difference gradually decreases, and when the pressure drop is smaller than the critical value, the sampling flow decreases as the pressure in the tank increases, so that the requirement of maintaining constant flow in the whole sampling period cannot be satisfied. Figure 1 shows the flow rate of the sample as a function of pressure in the sample tank (6 liter tank 3 hours of sampling) using a classical flow restricting needle valve of the united states sewei twink. As can be seen from fig. 1, in the preset sampling duration of 3 hours, the flow-limiting needle valve can only maintain the constant flow about 20 minutes just before the sampling begins, and then the sampling flow begins to decrease along with the increase of the pressure in the sampling tank, so that the requirement of constant-flow sampling is not met any more. Obviously, the use of the current limiting needle valve is a rough sampling mode, and the requirement of constant current sampling of an average sample is basically not met.
2. A mass flow controller (Mass Flow Controller) is employed to actively control the flow rate of gas into the sample tank. The method has the advantage of being free from the influence of the pressure in the tank, and can control the constant sampling flow in the whole sampling time. This approach then has at least three disadvantages: (a) The need for a dedicated sampling device based on a mass flow controller is costly and requires periodic calibration; (b) Mass flow controllers typically use the principle of thermal conduction and diffusion to measure the flow of gas and make real-time adjustments, and power must be supported throughout the sampling process, which is a challenge for field sites where power is inconvenient. Although a large-capacity battery can be used, for long-time sampling, for example, a sample with a sampling time length of one week, the electric quantity required for maintaining the constant flow is large, and the actual operability is poor; (c) The mass flow controller has many O-rings and sealing elements for sealing at the internal links and valves, and these elements are mostly made of organic materials, so that they can easily adsorb or release compounds into the collected VOCs sample, thus causing sample pollution.
3. The flow is controlled by frequent switching of the solenoid valve. The principle of the method is that an electromagnetic valve is arranged in a gas path, and the reduction of gas flow caused by pressure difference reduction is compensated by controlling the switching time of the electromagnetic valve (CN 208125450U is an automatic sampling device for constant flow of ambient air). The disadvantages of this method are: (a) Sampling is only performed when the electromagnetic valve is opened, and sampling is stopped when the battery valve is closed, so that strictly speaking, the collected samples are scattered samples in the sampling time period, and the samples are distributed uniformly but are not really average samples; (b) The solenoid valve maintenance switch and its control elements require a high power supply support, which is limited in operability by the power supply of the power outlet for long-term averaging, such as Zhou Yang; (c) The solenoid valve has lubricating oil and organic sealing material inside, and these materials can adsorb or release compound easily to the collected VOCs sample to pollute the sample.
Disclosure of Invention
The invention aims to solve the technical problem of providing a constant-flow sampling flow-limiting valve which can be used for maintaining constant flow in the sampling process.
In order to solve the technical problems, the invention discloses a constant-current sampling flow limiting valve, which comprises a flow limiting hole and a main valve body, wherein the flow limiting hole is communicated with an air inlet, the main valve body comprises a main cover body and a rear cover, two cavities are arranged in the main cover body, one cavity is a through air channel, one end of the air channel is communicated with the flow limiting hole, and the other end of the air channel is provided with a sampling tank interface which can be communicated with a sampling tank; the other is a space between the main cover body and the rear cover, an elastic membrane is arranged in the space, the elastic membrane is in sealing contact with the main cover body, and an elastic cavity is reserved between the elastic membrane and the wall of the air passage channel; the rear cover is positioned at the outer side of the elastic membrane and is fixed with the main cover body; wherein, the restriction orifice is fixed in the joint of 1/4 inch Shiwei lock (or its compatible type) by cold pressing method, in order to facilitate the mutual exchange between the restriction orifices of different apertures. And (3) marking a restricted hole mark outside the cold-pressed and packaged Shiwei Luok joint so as to be convenient for identification. After the treatment, the same flow limiting valve can be suitable for different flow range requirements by replacing the flow limiting hole. The sampling tank interface adopts a 1/4 inch pipe as the downstream sampling tank interface. This interface may be designed as a male or female connector of the world's wide rock (or its compatible type), or as a quick connector type, as desired.
A piston type nozzle is arranged in the air passage, and the air passage is partitioned into an air inlet section and an air outlet section by the piston type nozzle;
The air inlet section of the air channel is communicated with the elastic cavity, and the elastic cavity is communicated with the air outlet section of the air channel through the piston type nozzle;
the rear cover is provided with an atmospheric pressure balance port.
Further, the air inlet is provided with a particulate filter filled with a stainless steel sintered sheet filter material with a pore diameter of 1-7 μm so as to prevent particulate matters in the air sample from blocking the limiting hole and polluting the air sample, and the pore diameter of the stainless steel sintered filter core is 1-7 μm, most preferably 2 μm, and less preferably 5 μm, and most preferably 7 μm.
Further, the particulate filter is connected with the limiting hole through a sample injection bent pipe.
Further, a diaphragm pressing gasket is arranged between the elastic diaphragm and the rear cover, and presses the periphery of the elastic diaphragm.
Further, the outside of main lid still is provided with bellied screw hole post, and piston nozzle has a screw thread end, and this screw thread end is located this screw hole post, still is connected with adjusting bolt in the screw hole post, and the inner of this adjusting bolt supports the screw thread end of piston nozzle, and the outer end is equipped with the protection nut.
Further, a clamping piece is further arranged in the air channel, and the piston type nozzle is fixed to the clamping piece.
The nozzle adopts a piston type structure and can slide along a center cavity channel formed by the threaded hole column and the inner channel of the clamping piece. The flow can be regulated in a certain range by regulating the distance between the regulating bolt and the elastic membrane. When the adjustment is finished, the protection screw cap is covered to prevent the protection screw cap from being touched by mistake to move. The piston type nozzle and the air passage channel and the clamping piece are sealed by two nozzle O-shaped rings. To reduce contamination of the sample, the O-ring is preferably a polyfluoro material such as polytetrafluoroethylene or Viton O-ring.
Further, the periphery of the elastic diaphragm is arranged on one side of the elastic cavity and is sealed with the main cover body through a diaphragm sealing O-shaped ring.
Further, the main valve body is also provided with a pressure gauge interface which is connected with the main cover body and is communicated with the air outlet section of the air channel. The vacuum pressure composite meter can be arranged on the pressure meter interface and used for indicating the pressure in the tank body in the sampling process. The pressure gauge interface can be positioned at any position on the main cover body according to attractive and balanced requirements, and only the air outlet section of the air channel is communicated, so that the functions of the pressure gauge interface are not affected.
Further, the parts of the constant-current sampling flow limiting valve, which are in contact with sampling air, are all made of 316 type stainless steel castings, and the elastic diaphragm is made of soft 316 type stainless steel sheets. The device comprises a particulate filter, a sample injection bent pipe, a flow limiting hole, a main cover body of a main valve body, a piston type nozzle (or called a suction nozzle), a stainless steel elastic diaphragm and a sampling tank interface, wherein the main cover body is made of 316 stainless steel. Because the main parts are all 316 stainless steel, silanization passivation treatment can be carried out, and the requirement of VOCs sampling is met.
Further, the central part of the elastic membrane is a flat surface, and the rest parts are wavy surfaces.
The flow limiting valve is used as sampling equipment, and all parts contacted with the sampling gas can be passivated to ensure the accuracy of sampling analysis, and the flow limiting valve comprises a particulate filter, a sampling elbow, a flow limiting hole, a main cover body of a main valve body, a piston nozzle (or suction nozzle), a stainless steel elastic diaphragm and the like, and the diaphragm sealing O-shaped ring is made of a polyfluoro material, such as polytetrafluoroethylene or Viton O-shaped ring. The parts which are not in direct contact with the sample, such as the diaphragm pressing gasket and the rear cover of the main valve body, can be not subjected to silanization passivation treatment, but the silanization passivation treatment can be performed on all parts for the aesthetic sense of the whole valve because the silanization treatment can be used for coating the metal surface with a layer of purple red or deep blue with metal texture. However, the silanization passivation treatment only makes the flow limiting valve suitable for sampling VOCs, and does not affect the constant flow function of the flow limiting valve.
To reduce the effect on flow caused by changes in atmospheric temperature during field sampling, the orifice is made of a material having a small coefficient of thermal expansion. Materials meeting this condition and having low cost are preferably artificial ruby (corundum as the main component, chemical formula α -Al 2O3, red in color due to a small amount of chromium-containing compound mixed therein) and artificial sapphire (corundum as the main component, chemical formula α -Al 2O3, blue in color due to a small amount of titanium-containing compound mixed therein). The secondary material is invariable steel (also called invar alloy, invar steel and constant steel) with small thermal expansion coefficient. The flow restricting holes have different pore sizes corresponding to different sampling flow rates. Typically, the restriction orifice diameter is from 0.02 to 0.2mm. Wherein, the aperture of 0.02mm corresponds to the flow range of 0.5-7 mL/min;0.04 The flow range of the aperture of the mm is 2-15 mL/min; the aperture of 0.07mm corresponds to the flow range of 5-25 mL/min; the aperture of 0.11mm corresponds to the flow range of 13-60 mL/min; the aperture of 0.21mm corresponds to the flow range of 50-500 mL/min. The pore diameters of the small holes of each level are selected so as to cover the whole common sampling flow range (table 1) from 0.5 to 500mL/min on one hand, and the covering flow ranges of the small holes of each level need to be crossed to a certain extent due to certain errors in the processing of the pore diameters on the other hand. In addition, in the process of manufacturing the restriction hole, the actual flow rate may be different from the above-described one due to an aperture error, a difference in aperture shape, a difference in aperture length (thickness of the small hole in a direction perpendicular to the aperture surface), and the like. But the principle and thought of aperture selection are communicated.
The constant flow control of the flow is carried out by two steps: the first step, the flow rate is controlled within a certain range by using a flow limiting hole; the flow restricting holes with different apertures correspond to different flow ranges. And secondly, carrying out secondary adjustment on the flow through the piston type nozzle and the elastic membrane. With the sampling, the pressure in the tank will gradually rise, and the distance between the elastic diaphragm and the piston nozzle is gradually increased (automatically adjusted) under the action of pressure, so as to automatically compensate the flow reduced by the smaller upstream-downstream pressure difference. The constant sampling flow is maintained in the whole sampling time by the synergistic effect of the elastic diaphragm and the piston type nozzle. The invention is based on the flow limiting hole, and the device further stabilizes the flow by utilizing the cooperation of the elastic membrane and the piston type nozzle, which is a great improvement of the traditional flow control by only using the flow limiting hole.
In summary, the invention has the following characteristics: 1. and the pure mechanical component is free from power supply support, and is suitable for sampling in any place in the field. 2. The common sampling tank sampling flow range is 0.5-500 mL/min by changing the limiting holes with different apertures and adjusting the distance between the nozzle and the elastic membrane. 3. The secondary regulation is performed by a piston nozzle and an elastic diaphragm for pressure compensation. The elastic diaphragm automatically adjusts the distance between the elastic diaphragm and the piston type nozzle according to the pressure in the tank, so that the gas quantity sprayed by the nozzle is influenced, and the constant sampling flow in the whole sampling time period is maintained through the synergistic effect of the elastic diaphragm and the piston type nozzle. The method ensures that the gas flow rate from the ambient air to the sampling tank is kept constant (not changed or changed little due to the rising of the pressure in the tank) in the rising process of the vacuum in the sampling tank from 30inHg (initial vacuum) to 3inHg (terminating weak vacuum), thereby meeting the sampling requirement of average samples.
Drawings
FIG. 1 is a graph showing the variation of canister sampling flow rate with sampling time using a needle valve (orifice);
FIG. 2 is a schematic diagram of the overall structure of the restrictor valve of the present invention;
FIG. 3 is an enlarged schematic cross-sectional view of a main valve body of the restrictor valve of the present invention;
FIG. 4 is an exploded view of the main valve body of the present invention;
FIG. 5 is a schematic diagram of the structure of the constant current sampling restrictor valve of the present invention applied to a sampling tank;
FIG. 6 is a statistical chart of the 3h sampling flow results after the 3L sampling tank adopts the constant-flow sampling flow limiting valve of the invention.
Reference numerals in the drawings: 1-a particulate filter; 1.1-protecting the cap; 2-sample injection bent pipe; 3-flow restricting holes; 4-a main valve body; 4.1-adjusting bolts; ; 4.2-a main cover; 4.2.1-an air inlet section; 4.2.2-outlet sections; 4.2.3-the walls of the gas path channels; 4.3-piston nozzle; 4.3.1-nozzle inlet passages; 4.3.2-nozzle outlet channels; 4.3.3-nozzle O-rings; 4.4-diaphragm seal O-ring; 4.5-elastic membrane; 4.5.1-flattening the surface; 4.5.2-wave surface; 4.6-a diaphragm compression gasket; 4.6.1-pad vent holes; 4.7-a rear cover; 4.7.1-barometric pressure equalizing port; 4.8-elastic chambers; 4.9-clamping firmware; 4.9.1-clamping the firmware air flue; 4.10-threaded hole columns; 4.11-protecting nuts; 5-a pressure gauge interface; 5.1-a vacuum pressure compound meter; 6-a sampling tank interface; 7-sampling tank.
Detailed Description
The present invention will be described in further detail with reference to examples.
As shown in FIG. 2, the constant-flow sampling flow limiting valve mainly comprises a particulate filter 1 arranged at an air inlet, wherein a stainless steel sintered sheet filter material with the aperture of 1-7 μm is filled in the particulate filter 1, the aperture of 2 μm is the best, and particles larger than 2 μm in a gas sample are removed, so that the downstream flow limiting hole is prevented from being blocked by the particulates and the collected gas sample is prevented from being polluted (VOCs are released into the gas sample in the storage process of the particulates). The particulate filter 1 is connected with a limiting hole 3 through a sample injection bent pipe 2, the limiting hole 3 is communicated with a main valve body 4, and the main valve body 4 is shown in figures 3 and 4. The main valve body 4 comprises a main cover body 4.2 and a rear cover 4.7 covered on one side of the main cover body 4.2, an atmospheric pressure balance port 4.7.1 is formed in the rear cover 4.7, the atmospheric pressure balance port 4.7.1 is communicated with the inside, namely, a space between the rear cover 4.7 and the main cover body 4.2, an elastic diaphragm 4.5 and a diaphragm pressing gasket 4.6 are arranged in the space, the inner side of the periphery of the elastic diaphragm 4.5 is in sealing contact with the main cover body 4.2 through a diaphragm sealing O-shaped ring 4.4, a convex strip is arranged on the inner side of the periphery of the diaphragm pressing gasket 4.6, and the middle part and the outer side of the periphery of the convex strip pressing the elastic diaphragm 4.5 are propped against and fixed by the convex strip and the convex plate arranged at corresponding positions on the rear cover 4.7. The diaphragm pressing gasket 4.6 is also provided with a gasket vent hole 4.6.1 for the circulation of the atmosphere. The central part of the elastic membrane 4.5 is a flat surface 4.5.1, and the rest parts are wavy surfaces 4.5.2.
The elastic membrane 4.5 and the membrane pressing gasket 4.6 are both on the inner side of one side far away from the rear cover 4.7, and on the outer side of the other side.
The main valve body 4 is also provided with a cavity independent of the space between the rear cover 4.7 and the main cover 4.2, and is a through air passage, one end of the air passage is communicated with the flow limiting hole 3, the other end of the air passage is provided with a sampling tank interface 6 which can be communicated with a sampling tank, the middle part of the air passage is provided with a clamping piece 4.9, the air passage is partitioned into an air inlet section 4.2.1 and an air outlet section 4.2.2, the clamping piece 4.9 is internally and fixedly provided with a movable piston type nozzle 4.3 (or called a suction nozzle), the piston type nozzle 4.3 is provided with a threaded end, the threaded end is in threaded connection with a threaded hole column 1.10, and the threaded hole column 1.10 is arranged outside the main cover 4.2 in a protruding way. An adjusting bolt 4.1 is further connected in the threaded hole column 1.10, the inner end of the adjusting bolt 4.1 props against the threaded end of the piston nozzle 4.3, and a protecting nut 4.11 is arranged at the outer end. Two O-rings are provided on the piston nozzle 4.3 forming a seal between the fastener 4.9 and the airway passage. The air passage is parallel to the space between the rear cover 4.7 and the main cover body 4.2, an elastic cavity 4.8 is reserved between the air passage wall 4.2.3 and the elastic membrane 4.5, and the elastic cavity 4.8 is communicated with the air inlet section 4.2.1 of the air passage through an air vent arranged on the air passage wall 4.2.3.
A nozzle air inlet channel 4.3.1 communicated with the elastic cavity 4.8 is arranged in the piston type nozzle 4.3, a nozzle air outlet channel 4.3.2 is also arranged in the piston type nozzle 4.3, a clamping piece air channel 4.9.1 is arranged on one side of the clamping piece 4.9, one end of the nozzle air outlet channel 4.3.2 is communicated with the air inlet channel 4.3.1, the other end is communicated with the clamping piece air channel 4.9.1, and the other end of the clamping piece air channel 4.9.1 is communicated with an air outlet section 4.2.2 of the air channel. The outlet of the air outlet section 4.2.2 is provided with a sampling tank interface 6, the sampling tank interface 6 is used for connecting with an air inlet of a sampling tank, and the sampling tank interface 6 is a 1/4 inch pipe.
All parts contacted with the sampling air adopt 316 type stainless steel castings, and comprise a particulate filter 1, a sample injection bent pipe 2, a flow limiting hole 3, a main cover body 4.2, an elastic membrane 4.5, a piston type nozzle 4.3, a clamping piece 4.9 and a sampling tank interface 6.
In order to monitor the pressure in the sampling tank in real time, a pressure gauge interface 5 is also connected to the main valve body 4, and the pressure gauge interface 5 is positioned on the main cover body 4.2 and is communicated with the air outlet section 4.2.2 of the air channel. The elastic membrane 4.5 is made of a soft 316 stainless steel sheet.
When the constant-current flow-limiting sampling valve is not in use, the air inlet end of the particulate filter 1 is covered by a protective cap 1.1.
The main valve body 4 adopts a flat disc structure, the elastic membrane 4.5, the membrane pressing gasket 4.6 and the rear cover 4.7 are all round, and the membrane sealing O-shaped ring 4.4 is circular.
The sampling gas is filtered by the particulate filter 1, passes through the sample injection bent pipe 2, is subjected to primary flow restriction at the flow restriction hole 3, mainly limits the approximate range of flow, then enters the main valve body 4 of the flow restriction valve, is subjected to secondary flow control, and finally flows into a downstream sampling tank. In the secondary flow control, the flow is compensated by the synergistic effect between the elastic membrane 4.5 and the piston nozzle 4.3, so that the flow is constantly at a fixed set value, and constant flow is realized. The fixed value of this flow rate is related to the preset distance between the piston nozzle 4.3 and the elastic membrane 4.5, and the position of the piston nozzle 4.3 can be controlled by adjusting the position of the adjusting bolt 4.1. The constant current compensation principle is that the elastic diaphragm 4.5 is an elastic soft stainless steel metal sheet, the right side is communicated with the atmosphere because of the diaphragm pressing gasket 4.6 and always bears the pressure of one atmosphere, and the left side is communicated with the tank body of the sampling tank through the piston type suction nozzle 4.3. The pressure (vacuum, negative pressure) in the tank is transferred to the flat surface 4.5.1 in the central part of the elastic membrane 4.5 through the piston nozzle 4.3. The gas enters the tank body of the sampling tank from right to left (shown in fig. 3) through the piston type nozzle 4.3, suction force is generated on the left side of the elastic membrane 4.5, and when the vacuum in the sampling tank is stronger, the suction force is also stronger, so that the elastic membrane 4.5 protrudes leftwards, the air flow entering the piston type nozzle 4.3 is reduced, and the self-adjusting function is realized. As the sampling proceeds, the pressure in the tank will gradually rise, and the mechanical elastic force of the elastic diaphragm 4.5 rebounded rightward will gradually pull the elastic diaphragm 4.5 back to the right, increasing the distance between the piston nozzle 4.3 and the elastic diaphragm 4.5, thereby increasing the inhaled air flow of the piston nozzle 4.3. By combining the flow limitation of the flow limiting hole 3 and the elasticity of the elastic membrane 4.5, the constant flow in the sampling process can be automatically realized. The specific flow rate of this constant flow can be adjusted within a certain range by adjusting the position of the adjusting bolt 4.1 and the relative position of the piston nozzle 4.3 to the elastic membrane 4.5. When the piston nozzle 4.3 is close to the elastic membrane 4.5, the constant flow decreases, whereas when the piston nozzle 4.3 is far from the elastic membrane 4.5, the constant flow increases. That is, after the constant flow sampler is prepared, the level (flow range) of the constant flow can be changed by changing the size of the upstream flow limiting hole 3, and the distance between the downstream piston nozzle 4.3 and the elastic membrane 4.5 can be adjusted, so that the specific flow can be adjusted in the flow level.
Example 1
As shown in fig. 5, the constant-current sampling flow-limiting valve of the present invention is applied to a sampling tank 7. The sampling tank interface 6 of the constant-current sampling flow limiting valve is fixedly connected with the air inlet of the sampling tank 7. After the orifice 3 of one specification has been determined, the specific flow of the restrictor valve can be adjusted by rotating the adjusting bolt 4.1. After the flow has been adjusted, a protective screw cap 4.11 can be applied for fixing the position of the piston nozzle 4.3 (and thus the sampling flow).
The protection cap 1.1 is opened to sample the average sample.
The constant current performance of the constant current sampling flow limiting valve is tested: when a 3 liter tank is used for sampling for 3 hours, the flow limiting hole 3 is a sapphire flow limiting hole with the aperture of 0.07mm, the flow of the flow limiting valve is regulated to 14.4mL/min, and the flow measurement is carried out on the whole sampling process, and the result is shown in fig. 6. As can be seen from FIG. 6, in the sampling time of 3 hours, the flow-limiting valve can stably and constantly flow at about 14.4mL/min of the target flow, and the constant-flow sampling requirement is really met. The flow of the sample maintained can be stabilized for about 200 minutes, at this time, the sampling tank is basically full, the vacuum degree is only about 3inHg, and the flow begins to drop rapidly.
Claims (10)
1. A constant-current sampling flow limiting valve is characterized in that: the constant-current sampling flow limiting valve comprises a flow limiting hole and a main valve body, wherein the flow limiting hole is communicated with an air inlet, the main valve body comprises a main cover body and a rear cover, two cavities are arranged in the main cover body, one cavity is a through air passage, one end of the air passage is communicated with the flow limiting hole, and the other end of the air passage is provided with a sampling tank interface which can be communicated with a sampling tank; the other is a space between the main cover body and the rear cover, an elastic membrane is arranged in the space, the elastic membrane is in sealing contact with the main cover body, and an elastic cavity is reserved between the elastic membrane and the wall of the air passage channel; the rear cover is positioned at the outer side of the elastic membrane and is fixed with the main cover body;
A piston type nozzle is arranged in the air passage, and the air passage is partitioned into an air inlet section and an air outlet section by the piston type nozzle;
The air inlet section of the air channel is communicated with the elastic cavity, and the elastic cavity is communicated with the air outlet section of the air channel through the piston type nozzle;
the rear cover is provided with an atmospheric pressure balance port;
The pressure in the sampling tank is negative pressure; the elastic diaphragm automatically adjusts the distance between the elastic diaphragm and the piston type nozzle according to the pressure in the tank, so that the gas quantity sprayed by the piston type nozzle is influenced, and the constant sampling flow in the whole sampling time period is maintained through the synergistic effect of the elastic diaphragm and the piston type nozzle.
2. The constant flow sampling restrictor valve of claim 1, wherein: the air inlet is provided with a particulate filter, and the particulate filter is filled with stainless steel sintered sheet filter materials with the aperture of 1-7 mu m.
3. The constant flow sampling restrictor valve of claim 2, wherein: the particulate filter is connected with the limiting hole through a sample injection bent pipe.
4. The constant flow sampling restrictor valve of claim 1, wherein: and a diaphragm pressing gasket is further arranged between the elastic diaphragm and the rear cover, and presses the periphery of the elastic diaphragm.
5. The constant flow sampling restrictor valve of claim 1, wherein: the piston type spray nozzle is characterized in that a protruding threaded hole column is further arranged on the outer side of the main cover body, the piston type spray nozzle is provided with a threaded end, the threaded end is located in the threaded hole column, an adjusting bolt is further connected in the threaded hole column, the inner end of the adjusting bolt abuts against the threaded end of the piston type spray nozzle, and a protection nut is arranged at the outer end of the adjusting bolt.
6. The constant flow sampling restrictor valve of claim 1, wherein: and a clamping piece is further arranged in the air passage, and the piston type nozzle is fixed to the clamping piece.
7. The constant flow sampling restrictor valve of claim 1, wherein: the periphery of the elastic diaphragm is arranged on one side of the elastic cavity and is sealed with the main cover body through a diaphragm sealing O-shaped ring.
8. The constant flow sampling restrictor valve of claim 1, wherein: the main valve body is also provided with a pressure gauge interface which is connected with the main cover body and is communicated with the air outlet section of the air channel.
9. The constant flow sampling restrictor valve of claim 1, wherein: the central part of the elastic membrane is a flat surface, and the rest parts are wavy surfaces.
10. The constant flow sampling restrictor valve of claim 1, wherein: the parts of the constant-current sampling flow limiting valve, which are contacted with the sampling air, are all made of 316 stainless steel castings, and the elastic diaphragm is made of soft 316 stainless steel sheets.
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| CN112697546A (en) * | 2020-12-08 | 2021-04-23 | 成都市环境保护科学研究院 | Laminated micro-flow hole negative pressure gas sample collecting device and method |
| CN113431523B (en) * | 2021-07-30 | 2022-09-13 | 牡丹江北方油田机械有限公司 | Kelly bar plug valve for oil exploitation construction |
| CN114184434A (en) * | 2021-11-04 | 2022-03-15 | 苏州热工研究院有限公司 | Portable aerosol particle sampling device for nuclear power |
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