Over the last several weeks we discussed the feared NPSH and showed it is rarely an issue at design conditions. More often than not, noise and pressure problems are caused by air in the suction piping system. The suction pipe, in many cooling pumping systems, is under very little pressure. In fact, the suction of the pump could be under a vacuum. [Read more…]
Last week the R. L. Deppmann Monday Morning Minute gave an example of a pump selection for which we applied the margin multipliers to arrive at 24.5 feet of net positive suction head required or NPSHR. Now let’s turn our attention to the cooling tower pump suction piping and net positive suction head available or NPSHA. [Read more…]
Last week the R. L. Deppmann Monday Morning Minute defined NPSHR, and ended with the Hydraulic Institute (HI) definition as the absolute pressure that will cause the total head of the pump to be reduced by 3%, due to flow blockage from cavitation”. Of importance is the fact that it does not say that NPSHR is where cavitation begins. [Read more…]
Most cooling tower designs and installations are commissioned without any issues. The few percent of times where problems arise will cause multiple meetings, emails, finger pointing, and added costs. The issues are not caused by bad luck or bad Karma; tower water pumping issues are typically caused by air, dirt, or improper application. [Read more…]
Today, let’s look at a couple of selections and how the tank sizes and costs may vary based on location and type of tank selected. Our examples are shown in figures A & B. In each case we will use a system volume of 1500 gallons of water with a supply temperature of 200°F and 20°F ΔT. The system is 60 feet high and in each case the maximum pressure is 50 PSIG.
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Now we understand the difference between expansion and compression tanks as described in the R. L. Deppmann Monday Morning Minutes of 1-9-12 and 1-16-12. What happens to the formula results when comparing these two types of tanks? In part 1 of this series, we introduced the formula for tank sizing. The denominator of the equation was: (Pa /Pf) – (Pa /Po)
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What is the difference and when should I use them? Let’s start with ASME. In commercial and institutional applications, ASHRAE, as well as most codes require the pressure vessels carry an ASME U stamp. This assures the owner and the owner’s insurance carrier that the vessel was inspected by an independent appraiser and registered with the National Board. [Read more…]
[Continuation from last week’s MMM] Let’s assume we have a SIX story health care building and the heating system is 90 feet high with a 180 degree supply temperature. The pump and boilers are on the first floor. The BRYAN boilers selected come with 125 PSIG relief valves. Let’s also assume that the pump has a capacity of 800 GPM at 100 feet at design. [Read more…]
Maximum pressure in a hydronic system depends on a number of variables. Last week we used an example to introduce the maximum pressure at the expansion tank. Let’s look at a couple more examples. EXAMPLE TWO: Figure 1 shows a one line diagram of a heating system with a boiler and pumping system. [Read more…]
Cold fill pressure is defined as the initial pressure required to lift water from the point of the gauge readout to the top of the system plus 4 PSIG for positive venting. This statement holds true for systems from chilled water to heating systems up to 220°F. From 220°F to 250°F, consult the Bell and Gossett Air Management training manual, available from R L Deppmann Company, serving Michigan and Ohio, or from your local B&G representative for other parts of the globe. [Read more…]