A device for collecting particulates from air and other gases comprises a disposable impact disc and a filter downstream therefrom, the impact disc and filter being held in a readily dissembled and reassembled modular sequence. The air or other gas typically is moved through the collector at about ten liters per minute, and larger particles are collected on the impact disc while the smaller particles, generally desired as a sample for analysis or observation, are collected on the filter. Both the impact disc and the filter can be readily replaced.
The reader may be interested in the following US patents, which describe various air samplers, particulate collectors, and the like: Burghoffer U.S. Pat. No. 4,640,140, Marple U.S. Pat. No. 4,796,475, Jordan U.S. Pat. No. 6,692,553, John U.S. Pat. No. 5,437,198, Rodgers U.S. Pat. No. 5,404,762, Marple U.S. Pat. No. 5,040,424, Vennos U.S. Pat. No. 3,966,439, Lynch U.S. Pat. No. 4,675,034, Marple U.S. Pat. No. 4,872,779, and Nebash U.S. Pat. No. 3,957,469.
There is a demand for a portable, easily deployable, particulate matter sampler, for removing particulates from the air for inspection and analysis, especially particulates in the range of 0.1 to 100 μm in aerodynamic diameter, and typically below 10 μm aerodynamic diameter. Larger particles need to be screened or otherwise removed efficiently ahead of the filter in order to provide a clean collection of particles of the required size on the filter. Air flow is achieved by a pump chosen for the purpose, i.e. to draw air through the sampler at a rate of ten liters per minute, more or less; the pump may be battery operated so the sampler can be deployed in a somewhat remote area if desired, or so the sampler may be used to assess personal exposure.
Ideally the device will be easily dissembled so the filter and any member used for collecting larger particles (such as an impact disc having an adhesive coating) can be removed, observed, analyzed, and/or disposed of, while the filter and the impact disc may be replaced easily.
We have invented a particulate sampler that is simple and can be easily deployed, and which can be readily dissembled so the filter can be replaced, the large particle separator can be replaced, and the unit returned to service in a very short time, while the particle collections are taken to a laboratory or other facility for examination.
Our invention includes a device for collecting a sample of particulates from a gas, usually air, comprising (a) a housing including an inlet member and an outlet member for the gas and defining a flow path for the gas from the inlet member to the outlet member, the inlet member and the outlet member being normally attached to each other but readily separable, (b) a particle collecting assembly within the housing, the particle collecting assembly including a substantially planar particle impact disc, a support for the particle impact disc, a filter, and a support for the filter, the impact disc being situated substantially orthogonal to the flow path and including an adhesive coating, whereby particulates in the gas may impact on the impact disc and be retained thereon, the impact disc resting on the support for the impact disc and readily removable therefrom when the inlet member and the outlet member are separated, the filter resting on the filter support and being readily removable therefrom when the inlet member and the outlet member are separated, the filter being situated substantially orthogonal to the flow path and downstream in the flow path from the impact plate.
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The flow path proceeds through filter support 13, which is permeable or, in this case, a stainless steel screen having at least 30% open area for air to pass through without significant load on the pump. The air flow path then proceeds to the exit tube 5 and further to the pump, not shown, which is drawing the air through the entire apparatus.
It should be observed that the particle impact disc 20 and its support 18, and the filter 15 together with its support 13 form a particle collecting assembly within the inlet and outlet members 2 and 3 of the housing 1. The particle collecting assembly, including filter capsule bottom 11 are available for almost instant replacement as a whole as soon as the housing is taken apart by unscrewing inlet and outlet members 2 and 3. That is, not only are the oiled disc 20 and filter 15 readily replaced, but the entire sampler can be returned to use as soon as the particle collecting assembly is removed, by simply replacing it with a new one. After the filter is removed for analysis and replaced, and the impact disc replaced, the particle collecting assembly, or module, is ready for a new deployment.
In operation and use, the pump may be battery operated and the device may be left unattended for some time. However, our sampler is designed so that the particle impact disc, and the filter, can be readily removed and replaced, and the unit returned to work in a very short time. In one version, size and number of apertures 4 and the distance between the apertures 4 and the particle impact disc 20 are chosen so that the separation between the larger particles captured on the particle impact disc 20 and the smaller ones captured on the filter 15 is at about 10 μm aerodynamic diameter when the air flow is 10 liters per minute. Other separations may be accomplished and other flow rates may be used, as will be apparent to persons skilled in the art.
It is to be understood that our invention is not limited to the specific illustrated versions. For example, we have illustrated eight apertures 4, but they may be varied in size, number, and location, as is known in the art, they can be rectangular or of other shapes rather than circular. Generally, the inlet apertures 4 should direct the incoming air or other gas towards the particle impact disc. As another example of variability, the particle impact disc may be of a shape somewhat different from circular, but the particle impact disc should be impervious and capable of stopping and retaining the larger particles which strike it owing to their inertia in the moving air; for this purpose the impact disc may be made of a material having at least some adhesive properties and/or may be coated with oil or other material that will enhance its ability to retain particles.
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Another variation in the invention includes the possibility of employing various materials for the impact disc. These include quartz, fiber glass reinforced synthetic polymers, and Teflon; generally any substrate capable of capturing and retaining larger particles expected to be encountered in the particular environment to be monitored.
Our invention includes a device as described wherein particles greater than 2.51 μm aerodynamic diameter are captured on the impact disc and particles smaller than 2.5 μm aerodynamic diameter are captured on the filter at a gas flow rate through the flow path of 10 L/minute. More generally, our invention includes a device for collecting a sample of particulates from a gas comprising (a) a housing including an inlet member and an outlet member for the gas and defining a flow path for the gas from the inlet member to the outlet member, the inlet member and the outlet member being normally attached to each other but readily separable, (b) a particle collecting assembly within the housing, the particle collecting assembly including a substantially planar particle impact disc, a support for the particle impact disc, a filter, and a support for the filter, the impact disc being situated substantially orthogonal to the flow path, whereby particulates in the gas may impact on the impact disc and be retained thereon, the impact disc resting on the support for the impact disc and readily removable therefrom when the inlet member and the outlet member are separated, the filter resting on the filter support and being readily removable therefrom when the inlet member and the outlet member are separated, the filter being situated substantially orthogonal to the flow path and downstream in the flow path from the impact plate.
Our invention may be otherwise practiced within the scope of the following claims: