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Date Sept 2014 Ref M04 Theme Steam Dis Mechanical The Watchit!!! series are anonymously shared lessons learnt, near misses, and site issues that help us focus on why quality engineering matters. The devil is in the detail! To contribute, email Building Environments Helpdesk. All posted anonymously, unless the author wishes to be named! Steam Safety Valve Vent Size By George Riley The designing of Steam systems are not overly common in the world of MEP (Building Services) these days, particularly in the market sectors that we at BuroHappold operate. Having won a new project which would tap into a central steam plant this was my first opportunity to work with steam. Our central plant generates 120 PSI (Pounds per Square Inch) steam, in our case we want to use a Pressure Reducing Valve (PRV) arrangement to achieve 15 PSI. Below is my building loads based on a 2/3 and 1/3 split on the PRV arrangement. PRV 1, 1/3 load, 1,633 lb/hr & PRV 2, 2/3 load, 3,267 lb/hr The safety valve must be sized larger than the total load 4,900 lb/hr total load, in our case this was calculated to be 5,700 lb/hr. Based on this we selected a safety valve which required a 3” (80mm) inlet and a 4” (100mm) steam vent outlet. We then coordinated the route of the 4” steam vent outlet, 6” (150mm) when insulated from the basement mechanical room to the roof where it can discharge safety. When you select the safety valve you also require a you require a drip pan elbow and by code the discharge must be clear and unobstructed and can have no change in size. This meant that the steam vent line must overlap the drip pan elbow and will require to be the next pipe size up. In our case we needed to increase the steam vent to 6”, 8” insulated (200mm) and coordinate the route. We had recently approved the contractors installation drawings based on 4”. Thankfully we caught the error during the submittal review / approval process of the steam valves and before the vent was installed as it would have been extremely difficult and expensive to strip out replace. Moral of the story, when doing something new ask all the questions even the perceived “dumb” ones as a 4” discharge is not a the same as a 4” vent.
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DateSept 2014RefM04 ThemeSteamDisMechanical The Watchit!!! series are anonymously shared lessons learnt, near misses, and site issues that help us focus on why quality engineering matters. The devil is in the detail! To contribute, email Building Environments Helpdesk. ll posted anonymously, unless the author wishes to be named! Steam Safety Valve Vent SizeBy George Riley The designing of Steam systems are not overly common in the world of ME !B"ilding Services# these days$ partic"larly in the mar%et sectors that we at B"ro&appold operate' &aving won a new pro(ect which wo"ld tap into a central steam plant this was my first opport"nity to wor% with steam' )"r central plant generates 120 S* !o"nds per S+"are *nch# steam$ in o"r case we want to "se a ress"re Red"cing ,alve !R,# arrangement to achieve 1- S*' Below is my ."ilding loads .ased on a 2/0 and 1/0 split on the R, arrangement' R, 1$ 1/0 load$ 1$100 l./hr 2R, 2$ 2/0 load$ 0$213 l./hr The safety valve m"st .e si4ed larger than the total load 4$500 l./hr total load$ in o"r case this was calc"lated to .e -$300 l./hr'Based on this we selected a safety valve which re+"ired a 06 !70mm# inlet and a 46 !100mm# steam vent o"tlet' 8e then coordinated the ro"te of the 46 steam vent o"tlet$ 16 !1-0mm# when ins"lated from the .asement mechanical room to the roof where it can discharge safety' 8hen yo" select the safety valve yo" also re+"ire a yo" re+"ire a drip pan el.ow and .y code the discharge m"st .e clear and "no.str"cted and can have no change in si4e' This meant that the steam vent line m"st overlap the drip pan el.ow and will re+"ire to .e the ne9t pipe si4e "p' *n o"r case we needed to increase the steam vent to 16$ 76 ins"lated !200mm# and coordinate the ro"te' 8e had recently approved the contractors installation drawings .ased on 46' Than%f"lly we ca"ght the error d"ring the s".mittal review / approval process of the steam valves and .efore the vent was installed as it wo"ld have .een e9tremely diffic"lt and e9pensive to strip o"t replace' Moral of the story$ when doing something new as% all the +"estions even the perceived :d"m.6 ones as a 46 discharge is not a the same as a 46 vent'
