{"id":5537,"date":"2022-01-27T16:51:56","date_gmt":"2022-01-27T15:51:56","guid":{"rendered":"https:\/\/www.idro-elettrica.it\/esperto-risponde\/why-should-vertical-multistage-electric-pumps-preferably-be-used-only-under-positive-head-conditions\/"},"modified":"2026-07-01T09:47:40","modified_gmt":"2026-07-01T07:47:40","slug":"why-should-vertical-multistage-electric-pumps-preferably-be-used-only-under-positive-head-conditions","status":"publish","type":"esperto-risponde","link":"https:\/\/www.idro-elettrica.it\/en\/esperto-risponde\/why-should-vertical-multistage-electric-pumps-preferably-be-used-only-under-positive-head-conditions\/","title":{"rendered":"Vertical, submersible multistage electric pumps: why"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\"><em>Vertical submersible multistage electric pumps<\/em>: This is the recommended configuration when you want to reduce the risk of air in the inlet and malfunctions. Let\u2019s look at why, step by step, using a practical approach.* <br\/><\/p>\n\n<div class=\"wp-block-rank-math-toc-block\" id=\"rank-math-toc\"><h2>Table of Contents<\/h2><nav><ul><li class=\"\"><a href=\"#le-due-configurazioni-possibili-sotto-battente-e-soprabattente\">The two possible configurations: under-sash and over-sash<\/a><\/li><li class=\"\"><a href=\"#energia-potenziale-e-quota-zo-cosa-cambia-davvero\">Potential Energy and Zo Quota: What Really Changes<\/a><\/li><li class=\"\"><a href=\"#sotto-battente-pompa-adescata-e-pronta-a-partire\">Under the door: pump primed and ready to go<\/a><\/li><li class=\"\"><a href=\"#soprabattente-perche-serve-la-valvola-di-fondo\">Overflow: Why the Bottom Valve Is Needed<\/a><\/li><li class=\"\"><a href=\"#depressione-in-aspirazione-e-richiamo-daria-dallatmosfera\">Vacuum in the inlet and air intake from the atmosphere<\/a><\/li><li class=\"\"><a href=\"#accumulo-daria-nellimpianto-laccortezza-sulla-tubazione-di-aspirazione\">Air Buildup in the System: Precautions for the Inlet Line<\/a><\/li><li class=\"\"><a href=\"#elettropompe-multistadio-verticali-sotto-battente-il-punto-alto-interno\">Vertical, sub-flange, multistage electric pumps: the \u201chigh point\u201d inside<\/a><\/li><li class=\"\"><a href=\"#cosa-provoca-la-presenza-di-aria-tenuta-meccanica-prestazioni-e-disadescamento\">What Causes Air to Enter: Mechanical Seals, Performance, and Air Bleeding<\/a><\/li><li class=\"\"><a href=\"#conclusione-quando-e-consigliabile-utilizzare-queste-pompe\">Conclusion: When Is It Advisable to Use These Pumps?<\/a><\/li><\/ul><\/nav><\/div>\n\n<h2 id=\"le-due-configurazioni-possibili-sotto-battente-e-soprabattente\" class=\"wp-block-heading\">The two possible configurations: under-sash and over-sash<\/h2>\n\n<p class=\"wp-block-paragraph\">From a hydraulic standpoint, there are two possible configurations for operating a pump. The main difference is whether or not the hydraulic potential energy of the water in the inlet tank can be utilized. <\/p>\n\n<p class=\"wp-block-paragraph\">In practice, the <strong>Zo<\/strong> ratio can be:<\/p>\n\n<ul class=\"wp-block-list\">\n<li><strong>Positive<\/strong>: <strong>SOTTOBATTENTE<\/strong> condition<\/li>\n\n\n\n<li><strong>negative<\/strong>: <strong>OVERLAPPING<\/strong> condition<\/li>\n<\/ul>\n\n<p class=\"wp-block-paragraph\">This distinction affects how the pump appears before startup and how the inlet line behaves.<\/p>\n\n<h2 id=\"energia-potenziale-e-quota-zo-cosa-cambia-davvero\" class=\"wp-block-heading\">Potential Energy and Zo Quota: What Really Changes<\/h2>\n\n<p class=\"wp-block-paragraph\">The hydraulic potential energy of the water in the suction tank increases as <strong>Zo<\/strong> increases. It\u2019s a simple concept: the more \u201chead\u201d is available, the more the pump can benefit from the inlet conditions. <\/p>\n\n<p class=\"wp-block-paragraph\">When <strong>Zo is positive (below the waterline)<\/strong>, the system\u2019s design helps keep the machine ready to start. When <strong>Zo is negative (above the waterline)<\/strong>, the pump must already \u201cwork\u201d to draw water into its inlet. <\/p>\n\n<p class=\"wp-block-paragraph\">This difference is at the root of the typical problems associated with the upper beam.<\/p>\n\n<h2 id=\"sotto-battente-pompa-adescata-e-pronta-a-partire\" class=\"wp-block-heading\">Under the door: pump primed and ready to go<\/h2>\n\n<p class=\"wp-block-paragraph\">In the case of the <strong>SOTTOBATTENTE<\/strong> system, the inlet line and the machine are <strong>always full of water<\/strong>. Consequently: <\/p>\n\n<ul class=\"wp-block-list\">\n<li>The pump is <strong>primed<\/strong>.<\/li>\n\n\n\n<li>The pump is <strong>ready to start at any moment<\/strong><\/li>\n<\/ul>\n\n<p class=\"wp-block-paragraph\">This configuration reduces the likelihood of air pockets forming in the inlet and helps prevent unstable conditions during startup.<\/p>\n\n<h2 id=\"soprabattente-perche-serve-la-valvola-di-fondo\" class=\"wp-block-heading\">Overflow: Why the Bottom Valve Is Needed<\/h2>\n\n<p class=\"wp-block-paragraph\">In the case <strong>of an OVERFLOW system<\/strong>, the machine remains full only if there is a <strong>foot valve<\/strong> (a check valve located at the lower end of the Inlet pipe).<\/p>\n\n<p class=\"wp-block-paragraph\">This valve allows you to fill the system before the pump starts:<\/p>\n\n<ul class=\"wp-block-list\">\n<li>the <strong>inlet line<\/strong><\/li>\n\n\n\n<li>the <strong>pump itself<\/strong><\/li>\n<\/ul>\n\n<p class=\"wp-block-paragraph\">Without this condition, priming is not guaranteed, and startup may become problematic.<\/p>\n\n<h2 id=\"depressione-in-aspirazione-e-richiamo-daria-dallatmosfera\" class=\"wp-block-heading\">Vacuum in the inlet and air intake from the atmosphere<\/h2>\n\n<p class=\"wp-block-paragraph\">In an <strong>OVERHEAD<\/strong> configuration, the pump must overcome the force of gravity to draw water toward its inlet flange. To do so, <strong>it creates a vacuum in<\/strong> the inlet line, with an internal pressure lower than atmospheric pressure (<strong>P &lt; Po<\/strong>). <\/p>\n\n<p class=\"wp-block-paragraph\">This situation poses a specific risk: <strong>air<\/strong> may be <strong>drawn in from the atmosphere<\/strong> through the existing joints in the pipeline and between the valves.<\/p>\n\n<p class=\"wp-block-paragraph\">Once air enters, it does not \u201cdisappear\u201d; it tends to accumulate and create undesirable operating conditions.<\/p>\n\n<h2 id=\"accumulo-daria-nellimpianto-laccortezza-sulla-tubazione-di-aspirazione\" class=\"wp-block-heading\">Air Buildup in the System: Precautions for the Inlet Line<\/h2>\n\n<p class=\"wp-block-paragraph\">Air tends to accumulate at <strong>the highest points in the system<\/strong>. For this reason, it is important to ensure that inlet lines <strong>always run downward toward the pump<\/strong>, so that <strong>there are no high points upstream of the pump<\/strong>. <\/p>\n\n<p class=\"wp-block-paragraph\">The goal is simple: to prevent areas from forming where air can become stagnant, because these pockets can lead to malfunctions.<\/p>\n\n<p class=\"wp-block-paragraph\">In summary, in overhead installations, the geometry of the inlet piping becomes a critical factor that must be carefully managed.<\/p>\n\n<h2 id=\"elettropompe-multistadio-verticali-sotto-battente-il-punto-alto-interno\" class=\"wp-block-heading\">Vertical, sub-flange, multistage electric pumps: the \u201chigh point\u201d inside<\/h2>\n\n<p class=\"wp-block-paragraph\">In <strong>vertical multistage surface pumps<\/strong>, the design is such that <strong>a high point<\/strong> is created <strong>inside them<\/strong>. Specifically, air can accumulate right at the <strong>seal chamber (TM)<\/strong>. <\/p>\n\n<p class=\"wp-block-paragraph\">This is a key point for understanding the preference for the under-sash design: even if the inlet duct is properly maintained, the machine may have an internal area prone to air buildup.<\/p>\n\n<p class=\"wp-block-paragraph\">When air ends up where it shouldn&#8217;t, the effects can be immediate and harmful.<\/p>\n\n<h2 id=\"cosa-provoca-la-presenza-di-aria-tenuta-meccanica-prestazioni-e-disadescamento\" class=\"wp-block-heading\">What Causes Air to Enter: Mechanical Seals, Performance, and Air Bleeding<\/h2>\n\n<p class=\"wp-block-paragraph\">The presence of air prevents <strong>the mechanical seal<\/strong> from being <strong>lubricated<\/strong>, causing it to <strong>fail quickly<\/strong>.<\/p>\n\n<p class=\"wp-block-paragraph\">Furthermore, the amount of air can become so great that:<\/p>\n\n<ul class=\"wp-block-list\">\n<li><strong>reduce the pump&#8217;s performance<\/strong><\/li>\n\n\n\n<li>lead to a <strong>loss of<\/strong> interest<\/li>\n<\/ul>\n\n<p class=\"wp-block-paragraph\">De-biting can result not only in a complete loss of <strong>Q\/H output<\/strong>, but also in the <strong>mechanical destruction of the rotating parts<\/strong>.<\/p>\n\n<p class=\"wp-block-paragraph\">It is therefore a risk not only to performance but also to the integrity of the machine.<\/p>\n\n<h2 id=\"conclusione-quando-e-consigliabile-utilizzare-queste-pompe\" class=\"wp-block-heading\">Conclusion: When Is It Advisable to Use These Pumps?<\/h2>\n\n<p class=\"wp-block-paragraph\">For the reasons outlined above, it is advisable to use <strong>vertical multistage pumps<\/strong> (and, consequently, the pressurization units that use them) <strong>only when a hydraulically UNDERPRESSURE system is planned<\/strong>.<\/p>\n\n<p class=\"wp-block-paragraph\">In other words: if the system is set up to keep the inlet line and pump filled with water, this reduces the likelihood of air accumulation and the resulting consequences.<\/p>\n\n<p class=\"wp-block-paragraph\">If you&#8217;re considering the right configuration for your system, checking the plumbing layout (under-sill or over-sill) is a crucial first step.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Vertical sub-flange multistage electric pumps: here\u2019s why this configuration is preferable. Let\u2019s look at the differences compared to the over-flange type, the risks of air ingestion, and possible malfunctions. <\/p>\n","protected":false},"featured_media":5538,"parent":0,"template":"","meta":{"_acf_changed":false,"_angie_page":false,"footnotes":"","_members_access_role":[],"_members_access_error":""},"tags":[1314,1317,1318,1320,562,1321,1319,1316,1315],"class_list":["post-5537","esperto-risponde","type-esperto-risponde","status-publish","has-post-thumbnail","hentry","tag-electric-pumps","tag-grooming","tag-inlet-for-pumps","tag-mechanical-seal","tag-overhead","tag-pressurization-units","tag-system-air","tag-under-the-latch","tag-vertical-pumps"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.idro-elettrica.it\/en\/wp-json\/wp\/v2\/esperto-risponde\/5537","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.idro-elettrica.it\/en\/wp-json\/wp\/v2\/esperto-risponde"}],"about":[{"href":"https:\/\/www.idro-elettrica.it\/en\/wp-json\/wp\/v2\/types\/esperto-risponde"}],"version-history":[{"count":0,"href":"https:\/\/www.idro-elettrica.it\/en\/wp-json\/wp\/v2\/esperto-risponde\/5537\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.idro-elettrica.it\/en\/wp-json\/wp\/v2\/media\/5538"}],"wp:attachment":[{"href":"https:\/\/www.idro-elettrica.it\/en\/wp-json\/wp\/v2\/media?parent=5537"}],"wp:term":[{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.idro-elettrica.it\/en\/wp-json\/wp\/v2\/tags?post=5537"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}