{"id":7957,"date":"2020-11-03T16:19:00","date_gmt":"2020-11-03T15:19:00","guid":{"rendered":"https:\/\/www.idro-elettrica.it\/esperto-risponde\/parallel-tanks-rules-and-limits-for-water-reserves\/"},"modified":"2026-07-01T09:46:29","modified_gmt":"2026-07-01T07:46:29","slug":"parallel-tanks-rules-and-limits-for-water-reserves","status":"publish","type":"esperto-risponde","link":"https:\/\/www.idro-elettrica.it\/en\/esperto-risponde\/parallel-tanks-rules-and-limits-for-water-reserves\/","title":{"rendered":"Parallel Tanks: Rules and Limits for Water Reserves"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\"><em>Parallel tanks<\/em> as a water reserve: the answer isn\u2019t a simple \u201cyes\u201d or \u201cno.\u201d The key is to ensure <strong>the performance, continuity, and reliability<\/strong> of the water supply throughout its expected service life, even in the event of a fire. <\/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=\"#la-domanda-in-pratica-e-perche-e-delicata\">The question (basically) is why it&#8217;s a sensitive issue<\/a><\/li><li class=\"\"><a href=\"#cosa-dice-uni-tr-11438-riserva-idrica-come-riserva-unica\">What UNI\/TR 11438 Says: Water Supply as a \u201cSingle Reserve\u201d<\/a><\/li><li class=\"\"><a href=\"#serbatoi-in-parallelo-e-portata-di-progetto-il-punto-non-negoziabile\">Parallel Tanks and Design Flow Rate: The Non-Negotiable Point<\/a><\/li><li class=\"\"><a href=\"#cosa-dimensionare-uscite-serbatoi-e-collettori-di-aspirazione\">What to size: tank outlets and inlet manifolds<\/a><\/li><li class=\"\"><a href=\"#ambito-di-validita-quando-i-metodi-elementari-possono-bastare\">Scope of Application: When Elementary Methods Are Sufficient<\/a><\/li><li class=\"\"><a href=\"#quando-serve-un-approccio-ingegnerizzato-e-perche\">When an \u201cEngineered\u201d Approach Is Needed (and Why)<\/a><\/li><li class=\"\"><a href=\"#conclusione\">Conclusion<\/a><\/li><\/ul><\/nav><\/div>\n\n<h2 id=\"la-domanda-in-pratica-e-perche-e-delicata\" class=\"wp-block-heading\">The question (basically) is why it&#8217;s a sensitive issue<\/h2>\n\n<p class=\"wp-block-paragraph\">When it comes to multiple tanks connected in parallel, the key issue is not \u201chow many tanks,\u201d but <strong>how<\/strong> the system behaves during operation.<\/p>\n\n<p class=\"wp-block-paragraph\">This is a sensitive issue because, if the splitting is not managed properly, it can lead to a <strong>malfunction of the entire fuel supply system<\/strong>. For this reason, before adopting a solution with multiple tanks, a rigorous approach is needed: the goal is not simply to \u201cconnect tanks in parallel,\u201d but <strong>to ensure that the reserve remains truly available<\/strong> to the system. <\/p>\n\n<h2 id=\"cosa-dice-uni-tr-11438-riserva-idrica-come-riserva-unica\" class=\"wp-block-heading\">What UNI\/TR 11438 Says: Water Supply as a \u201cSingle Reserve\u201d<\/h2>\n\n<p class=\"wp-block-paragraph\">The key reference is UNI\/TR 11438 (4.2.3), which clarifies a fundamental concept: <strong>\u201cThe water reserve must be understood as a single reserve.\u201d<\/strong><\/p>\n\n<p class=\"wp-block-paragraph\">Consequently:<\/p>\n\n<ul class=\"wp-block-list\">\n<li><strong>Splitting the water supply into multiple parts should be avoided<\/strong>, as it can cause service disruptions.<\/li>\n\n\n\n<li><strong>Situations other than those involving a single water supply<\/strong> must be <em>engineered<\/em> to ensure that the system meets the required performance standards in all cases.<\/li>\n\n\n\n<li>The design must ensure <strong>the continuity and reliability<\/strong> of the water supply <strong>throughout its expected service life<\/strong>, even in the <strong>event of a fire<\/strong>.<\/li>\n\n\n\n<li>Availability must also be ensured in accordance with the provisions of <strong>section 4.1.1<\/strong>.<\/li>\n<\/ul>\n\n<p class=\"wp-block-paragraph\">In other words: the rules promote a \u201csingle\u201d reserve not out of abstract preference, but to reduce the operational risks typical of a fragmented system.<\/p>\n\n<h2 id=\"serbatoi-in-parallelo-e-portata-di-progetto-il-punto-non-negoziabile\" class=\"wp-block-heading\">Parallel Tanks and Design Flow Rate: The Non-Negotiable Point<\/h2>\n\n<p class=\"wp-block-paragraph\">The \u201csingle reserve\u201d principle gives rise to a very clear practical requirement: <strong>even at the minimum level, the tanks must be capable of delivering the design flow rate<\/strong>.<\/p>\n\n<p class=\"wp-block-paragraph\">This point is crucial because it shifts the focus from \u201ctotal\u201d capacity to <strong>the capacity that can actually be delivered<\/strong> under the worst-case conditions (i.e., when levels are at their lowest). Therefore, it is not enough for the sum of the volumes to be adequate: it must be verified that the system, as a whole, <strong>delivers the required flow rate<\/strong> without any loss of performance that would compromise the supply. <\/p>\n\n<h2 id=\"cosa-dimensionare-uscite-serbatoi-e-collettori-di-aspirazione\" class=\"wp-block-heading\">What to size: tank outlets and inlet manifolds<\/h2>\n\n<p class=\"wp-block-paragraph\">If you decide to use parallel tanks, the text emphasizes that at least the following components must <strong>be properly sized<\/strong>:<\/p>\n\n<ul class=\"wp-block-list\">\n<li><strong>the diameters of the tank outlets<\/strong><\/li>\n\n\n\n<li><strong>the diameter of the inlet manifolds<\/strong><\/li>\n<\/ul>\n\n<p class=\"wp-block-paragraph\">The reason is directly related to the required performance: if the outlets and manifolds are not properly sized, the design flow rate may not be guaranteed, especially under critical conditions (for example, <strong>at the minimum level<\/strong>).<\/p>\n\n<p class=\"wp-block-paragraph\">The text indicates that, through the following illustrations, it aims to provide <strong>basic calculation methods<\/strong> for determining the sizing of these components. The key point, however, is already clear: the \u201cparallel\u201d solution cannot be improvised and requires careful sizing of the connection\u2019s key components. <\/p>\n\n<h2 id=\"ambito-di-validita-quando-i-metodi-elementari-possono-bastare\" class=\"wp-block-heading\">Scope of Application: When Elementary Methods Are Sufficient<\/h2>\n\n<p class=\"wp-block-paragraph\">The \u201celementary\u201d calculation methods mentioned above apply within specific limits. In particular: <\/p>\n\n<ul class=\"wp-block-list\">\n<li><strong>No more than two tanks connected in parallel to the same manifold<\/strong><\/li>\n\n\n\n<li><strong>Collector length &lt;, 10 m<\/strong><\/li>\n<\/ul>\n\n<p class=\"wp-block-paragraph\">These conditions are not a mere detail: they define the scope within which the approach remains reasonable. If these limits are exceeded, the degree of approximation increases, and there is a risk of making design decisions that are not appropriate for the primary objective: ensuring the performance and continuity of the water supply. <\/p>\n\n<h2 id=\"quando-serve-un-approccio-ingegnerizzato-e-perche\" class=\"wp-block-heading\">When an \u201cEngineered\u201d Approach Is Needed (and Why)<\/h2>\n\n<p class=\"wp-block-paragraph\">The text is clear: in the case of:<\/p>\n\n<ul class=\"wp-block-list\">\n<li><strong>&gt; -2 Tanks 2<\/strong><\/li>\n\n\n\n<li><strong>&gt;, and 10 m manifold lengths<\/strong><\/li>\n<\/ul>\n\n<p class=\"wp-block-paragraph\">The approach described above (i.e., the elementary approach) <strong>would become too approximate<\/strong>.<\/p>\n\n<p class=\"wp-block-paragraph\">This is consistent with the principle cited in UNI\/TR 11438: <em>situations other than a single water supply must be engineered<\/em>. Here, \u201cengineered\u201d means designing the solution in such a way as to <strong>ensure<\/strong>: <\/p>\n\n<ul class=\"wp-block-list\">\n<li>performance requirements of the system;<\/li>\n\n\n\n<li>continuity and reliability of the water supply;<\/li>\n\n\n\n<li>availability for the entire expected duration;<\/li>\n\n\n\n<li>resistance to the effects of fire.<\/li>\n<\/ul>\n\n<p class=\"wp-block-paragraph\">It is therefore not a matter of \u201cdesign style,\u201d but rather of consistency with the safety objective and the reliability expected of the reserve.<\/p>\n\n<h2 id=\"conclusione\" class=\"wp-block-heading\">Conclusion<\/h2>\n\n<p class=\"wp-block-paragraph\">Using <strong>tanks in parallel<\/strong> as a water reserve is a matter that requires caution: the reserve should be treated as <strong>a single unit<\/strong>, and splitting it up should be avoided if it could cause service disruptions. If this approach is taken, the non-negotiable requirement is to ensure <strong>the design flow rate even at the minimum level<\/strong> by correctly sizing <strong>the tank outlets<\/strong> and <strong>inlet manifolds<\/strong>, paying particular attention to the specified applicability limits. <\/p>\n","protected":false},"excerpt":{"rendered":"<p>Parallel tanks as a water reserve: it\u2019s possible, but caution is needed because the reserve must be treated as a \u201csingle\u201d system. Let\u2019s see what UNI\/TR 11438 specifies and which checks are critical for flow rate, continuity, and reliability. <\/p>\n","protected":false},"featured_media":7959,"parent":0,"template":"","meta":{"_acf_changed":false,"_angie_page":false,"footnotes":"","_members_access_role":[],"_members_access_error":""},"tags":[695,551,658,696,694,698,697,570,553,646],"class_list":["post-7957","esperto-risponde","type-esperto-risponde","status-publish","has-post-thumbnail","hentry","tag-design-flow-rate","tag-engineering-insights","tag-fire-prevention","tag-inlet-manifold","tag-parallel-tanks","tag-system-reliability","tag-system-sizing","tag-uni-tr-11438","tag-water-supply","tag-water-supply-2"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.idro-elettrica.it\/en\/wp-json\/wp\/v2\/esperto-risponde\/7957","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\/7957\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.idro-elettrica.it\/en\/wp-json\/wp\/v2\/media\/7959"}],"wp:attachment":[{"href":"https:\/\/www.idro-elettrica.it\/en\/wp-json\/wp\/v2\/media?parent=7957"}],"wp:term":[{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.idro-elettrica.it\/en\/wp-json\/wp\/v2\/tags?post=7957"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}