{"id":38077,"date":"2024-02-05T16:49:24","date_gmt":"2024-02-05T16:49:24","guid":{"rendered":"https:\/\/www.alicat.com\/?post_type=article&p=38077"},"modified":"2026-02-16T22:27:44","modified_gmt":"2026-02-16T22:27:44","slug":"wahl-eines-instruments-zur-vermeidung-von-strahlenbildung-bei-massenflusskontrollgeraten-in-der-vena-contracta","status":"publish","type":"support","link":"https:\/\/www.alicat.com\/de\/support\/choosing-an-instrument-avoiding-jetting-in-mass-flow-controllers-the-vena-contracta\/","title":{"rendered":"Vermeidung von Strahlenbildung in Massendurchflussreglern: Die Vena Contracta"},"content":{"rendered":"\n[et_pb_section fb_built=”1″ _builder_version=”4.23.1″ _module_preset=”default” min_height=”2059.2px” custom_padding=”|0px|82px|0px|false|false” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_row _builder_version=”4.23.1″ _module_preset=”default” custom_padding=”5px|||||” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.23.1″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.23.1″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”]

Avoiding jetting in mass flow controllers: the vena contracta<\/strong><\/h1>\n

High flow mass flow controllers always need downstream valves and high flow meters can\u2019t be plumbed with small process ports.\u00a0\u00a0<\/span>\u00a0<\/span><\/p>\n

The reason for this is jetting. But what is jetting? What causes it? Why is it important for Alicat devices in particular and why is it mainly an issue in high flow devices?\u00a0<\/span>\u00a0<\/span><\/p>\n

To answer these questions, we need to first discuss what is happening as fluids pass through our valves.<\/span>\u00a0<\/span><\/p>\n

<\/span><\/p>\n

Categorizing flow through flow restrictions<\/h2>\n

In unrestricted laminar flow, fluid moves in a consistent and organized way. The flow channels run parallel in the direction of flow, such as in non-turbulent river and plumbing systems. The flow pattern is regular and easy to categorize.\u00a0<\/span><\/p>\n

As flow approaches any restriction, such as an orifice or a valve, the outer flow channels, or those\u00a0<\/span>farthest away from the restriction, start to bend towards the inner flow channels, or those nearest to the restriction. As flow reaches to the restriction, the inner flow accelerates as a result of condensing flow from the outer flow channels.\u00a0<\/span><\/p>\n

Just after the restriction, the outer flow channels continue to bend into the inner flow channels, resulting in continued narrowing and acceleration of the flow. Eventually,<\/span>\u00a0<\/span>flow begins to move back from the inner flow channels to fill out the outer flow channels, returning to normal flow.\u00a0 In other words, even though the flow path is again unrestricted and normal, the flow doesn\u2019t instantly correct itself. Instead, it takes a little distance and time to spread out again.\u00a0<\/span>\u00a0<\/span><\/p>\n

<\/span><\/p>\n

Vena contracta<\/h2>\n

Due to fluid momentum, as fluid passes a restriction such as an orifice or valve, it continues to compress itself. Since this momentum takes some time and distance to change back around to start expanding, the fluid\u2019s narrowest contraction point is just past the orifice or valve.\u00a0<\/span><\/p>\n

We refer to this narrowest flow point as the\u00a0vena contracta<\/strong>, which means \u201cnarrow veins\u201d in Latin. The term jetting is used to describe the phenomena of this unique, constricted flow pattern.\u00a0\u00a0<\/span>\u00a0<\/span><\/p>[\/et_pb_text][et_pb_image src=”https:\/\/www.alicat.com\/wp-content\/uploads\/2024\/04\/Jetting-vena-contracta.webp” title_text=”Jetting-vena-contracta” _builder_version=”4.23.1″ _module_preset=”default” width=”70%” module_alignment=”center” custom_padding=”20px||20px||false|false” global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_image][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” hover_enabled=”0″ global_colors_info=”{}” theme_builder_area=”post_content” sticky_enabled=”0″]

Adjusting for jetting in Alicat mass flow devices<\/h2>\nNow that we\u2019ve explained jetting and the vena contracta, let\u2019s discuss its implications for Alicat devices.<\/span>\u00a0<\/span>\n\nIn Alicat devices, jetting happens when high flow gases or liquids pass through Alicat valves, restricting the flow and taking some distance and time to refill the whole flow channel back up, since the vena contracta is located after the valve. If the flow remains constricted for too long and doesn\u2019t expand to fill the entire flow channel inside Alicat devices, then flow rates become inaccurate. Because the geometry that the flow follows is different than what the Alicat device is expecting, the values which the Alicat device reports for flow rate become largely meaningless.\u00a0<\/span>\u00a0<\/span>\n\nTo avoid problems which may occur because of jetting, Alicat devices at high flow rates use downstream valves and use larger orifices, reducing the distance that it takes for jetting to dissipate, ensuring that flow rate measurements are highly accurate since the jetting does not have an impact on the flow measurement.\u00a0<\/span>\u00a0<\/span>\n\nThis is not usually an issue which occurs in lower flow devices. Since the vena contracta\u2019s distance from the valve or orifice is dependent on flow rate, occurring closer to the valve or orifice at lower flow, at lower flow rates, flow can normalize primarily before reaching Alicat\u2019s laminar flow elements. With high flow rates, the vena contracta moves further downstream of the flow restriction, taking more distance to expand all the way back out.\u00a0<\/span>For this same reason, small process ports can\u2019t be used on high-flow devices, as there just isn\u2019t enough time for everything to expand back out.\u00a0<\/span>\u00a0<\/span>\n\n<\/span>\n

More support<\/h2>\nAlicat\u2019s application engineers are prepared to help you avoid jetting by picking the correct device configurations for your needs, ensuring consistent, accurate, and repeatable flow measurement and control.\u00a0<\/span>\u00a0<\/span>\n\n[\/et_pb_text][\/et_pb_column][\/et_pb_row][\/et_pb_section]\n","protected":false},"featured_media":46458,"parent":0,"template":"","meta":{"_acf_changed":false,"_et_pb_use_builder":"on","_et_pb_old_content":"","_et_gb_content_width":"1920","content-type":"","_searchwp_excluded":""},"categories":[],"class_list":["post-38077","support","type-support","status-publish","has-post-thumbnail","hentry"],"acf":[],"yoast_head":"\nAvoiding Jetting in Mass Flow Controllers: The Vena Contracta - Alicat Scientific<\/title>\n<meta name=\"description\" content=\"In Alicat devices, jetting happens when high flow gases or liquids pass through Alicat valves, restricting the flow and taking some distance and time to refill the whole flow channel back up.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.alicat.com\/de\/unterstutzung\/wahl-eines-instruments-zur-vermeidung-von-strahlenbildung-bei-massenflusskontrollgeraten-in-der-vena-contracta\/\" \/>\n<meta property=\"og:locale\" content=\"de_DE\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Avoiding Jetting in Mass Flow Controllers: The Vena Contracta\" \/>\n<meta property=\"og:description\" content=\"In Alicat devices, jetting happens when high flow gases or liquids pass through Alicat valves, restricting the flow and taking some distance and time to refill the whole flow channel back up.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.alicat.com\/de\/unterstutzung\/wahl-eines-instruments-zur-vermeidung-von-strahlenbildung-bei-massenflusskontrollgeraten-in-der-vena-contracta\/\" \/>\n<meta property=\"og:site_name\" content=\"Alicat Scientific\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/alicatscientific\/\" \/>\n<meta property=\"article:modified_time\" content=\"2026-02-16T22:27:44+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.alicat.com\/wp-content\/uploads\/2026\/01\/featured-alicat.png\" \/>\n\t<meta property=\"og:image:width\" content=\"1200\" \/>\n\t<meta property=\"og:image:height\" content=\"630\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"4\u00a0Minuten\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/www.alicat.com\\\/support\\\/choosing-an-instrument-avoiding-jetting-in-mass-flow-controllers-the-vena-contracta\\\/\",\"url\":\"https:\\\/\\\/www.alicat.com\\\/support\\\/choosing-an-instrument-avoiding-jetting-in-mass-flow-controllers-the-vena-contracta\\\/\",\"name\":\"Avoiding Jetting in Mass Flow Controllers: The Vena Contracta - 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