Category » Ask an Engineer

There were 29 articles found in this category:

1. What is NPSH for a tank open to atmosphere?
   Question: What is NPSH for a tank open to atmosphere? What would cause a negative pressure (vacuum) at the pump suction? Answer: The following explanation can be found in the upcoming second edition of Piping System Fundamentals, The Complete Guide to Gaining a Clear Picture of Your Piping Syste ...
2. Pump curves: accounting for suction / discharge elevation difference
   Question: There are often cases where the centerlines of the suction and discharge from a given pump are not on the same level. Some cases can be more significant than others. When the manufacturers create their curves, are they accounting for this change in elevation in the data? Answer: The H ...
3. What's NRPD and is it different from the metered dP reading?
   The latest version of the Crane Technical Paper 410 has a great writeup on the definition of these two types of differential pressures: Orifices, nozzles and venturi are used principally to meter rate of flow. Orifices are also used to restrict flow or to reduce pressure, and are commonly referr ...
4. Pumping into a Partially Full Pipeline
   Often it is necessary to pump into a pipeline that may or may not be full of liquid. A user was unable to get the needed results because the discharge pipeline in her system was full under high pumping demands, and partially full under low pumping demands. This article describes how to use PIPE- ...
5. What is the relationship in a pipeline between pressure drop and flow rate in a pipeline?
   Q. What is the relationship in a pipeline between pressure drop and flow rate in a pipeline? A. To answer this question we should look at the pressure drop equation as defined by the following formula taken from the Crane TP-410 equation 6-8 for flow rate in gpm. In looking at the above formu ...
6. Will the Flow Rate Double in the Remaining Valves If the Other Half Are All Closed?
   Q. I have a manifold that is 1” OD tubing with 24 outlets of ¼ inch tubing. A needle valve is installed in each of the ¼ inch branching lines and throttled to regulate a flow of ~3 cc/min. The supply pressure into the manifold is 100 psig. What will happen to the system if I close 12 of t ...
7. How Not to Save Energy by Installing a High Efficiency Motor
   As Seen in the June 2011 Issue of Plant Engineering Magazine Introduction The Energy Independence and Security Act of 2007 (EISA), which mandates that all new motors sold in the United States must meet a minimum motor efficiency, went into effect on December 19, 2010. The law doesn’t app ...
8. Piping System Brain Teaser #4: System Troubleshooting Part 2
   Piping System Brain Teaser #4: System Troubleshooting Part 2 Last month we looked at the operating conditions of a couple of systems to determine the root cause of a problem that was occurring in the system. This month we'll look at two more. To recap, a key aspect of troubleshooting a problem ...
9. Piping System Brain Teaser #2
   Brain Teaser #2: How does a fluid’s properties affect a centrifugal pump's performance? Manufacturers typically test centrifugal pumps with water to develop a pump performance curve that they provide to their customers. But what if a customer is using that pump for a fluid other than water ...
10. Piping System Brain Teaser #3
    Piping System Brain Teaser #3: System Troubleshooting Part 1 A key aspect of troubleshooting a problem in a piping system is knowing what the "normal" operating conditions are for the flow rates, pressures, valve positions, and other measured values in the system. If you don't know what is "nor ...
11. How Accurate is My PIPE-FLO and/or Flow of Fluids Model?
    Q: How Accurate is My PIPE-FLO and/or Flow of Fluids Model? PIPE-FLO (and/or Flow of Fluids) uses proven engineering concepts, equations, and methods to calculate results based on the data that is input by the user, but there are several things that may contribute to discrepancies between the ...
12. Piping System Brain Teaser #1
    Piping System Brain Teaser #1: Static Head Here at ESI we decided to introduce a new thread to the "Ask an Engineer" series: Piping System Brain Teasers! We'd like to test your understanding of piping systems and challenge the way you think about them. As engineers, we constantly apply our expe ...
13. What is suction specific speed and how can it be used in centrifugal pump selection?
    Q. What is suction specific speed and how can it be used in centrifugal pump selection? A. Suction specific speed is an index that describes the characteristics of the suction side of the impeller. It is calculated using the NPSHr in feet, speed (N) in rpm, and flow rate (Q) in gpm at the pump& ...
14. Should the pump affinity rules be used to correct pump curve data when trimming impellers?
    Q. Should I use the pump affinity rules to correct my pump curve data when trimming the impeller? A. While the affinity rules can give a good approximation of pump performance for a given impeller trim, in some cases the error can be as high as 15 to 20%. Generally speaking, lower specific spee ...
15. How to Share Selection Lists in PUMP-FLO Premium
    You can share a PUMP-FLO Premium selection list with anyone who has an email account. Share recipients don’t need a Premium subscription to view the list, but will need to create a user account if they don’t have one. Share recipients who have Premium subscriptions will be able to ma ...
16. Copying Identical Paths on the FLO-Sheet
    Often in a piping model multiple identical paths are present and must be entered in PIPE-FLO. Using PIPE-FLO's advanced drawing features piping systems with multiple paths can be created quickly. This article describes how to use the group copy, attaching nodes, and adding vertex features of P ...
17. How Pressure Independent Control Valves Work
    Introduction The Pressure Independent Control Valve (PICV) technology was brought to market 18 years ago. This technology has now matured and is accepted as a proven application for optimizing hydronic system delta T, enhancing system performance and reducing energy cost. A high quality, indus ...
18. Time Simulation with Overtime
    It is often necessary to see how a piping system operates over time. For example, as a tank is pumped down, the static head increases, resulting in a smaller flow rate through the pump. This reduction in flow rate causes the tank to take longer to pump down. This type of calculation is called an ...
19. Modeling Positive Displacement Pumps
    Both PIPE-FLO and Flow of Fluids can be used to model positive displacement (PD) pumps. PD pumps are modeled using a combination of a fixed flow pump and a slip component. This article reviews the operation of PD pumps and demonstrates how to create a slip component using an example pump opera ...
20. Static Head in Systems with Varying Fluid Temperatures
    Q. What is static head and how is the static head calculated for a system that contains a fluid at different temperatures? A. The static head of a system is that portion of the pump’s Total Head that must be added to the fluid before a single drop of fluid will move in the system. It is ...