Correction Of Vacuum Pump Capacity For Altitude

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All Vacuum Pump performance curves and technical data are referenced to barometric pressure at
Sea  level. When operating at higher altitudes, the barometric pressure is always lower, therefore
some calculations are required to correct for this pressure variation. Caution must be taken when specifying  a  pump at higher altitudes; the amount of vacuum desired cannot exceed the barometric pressure at that altitude.

Since the pump performance of a positive displacement pump is a function of pressure ratio:

P1/P2 at sea level = P1/P2 at altitude
(P2) at sea level = (P1) at sea level (P2) at altitude/(P1) at altitude

Example:  Select a vacuum pump for 200 CFM to be installed at an altitude of 2743 meters (approximately 9,000feet), and to operate at a vacuum of 15 in. Hg at that altitude using 60f.
water as service liquid.

Barometric pressure at 2743 meters is 551.5 mm Hg Abs, or 21.7 inch Hg absolute. Therefore an operating pressure of 15 inches at this altitude means an absolute pressure of 21.7 - 15.0 = 6.7 in. Hg Abs

The actual pressure ratio of the unit is:

P1/P2 at altitude = 21.7/6.7 = 3.238

Because pump performance basically is a function of pressure ratio, the selection should be made at the similar pressure ratio at sea level.

29.92/3.238= 9.24" Hg absolute

29.92 - 9.24= 20.68in. Hg vacuum or 9.24/29.92 x 760 = 235mm

Medical Surgical Vacuum System

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A medical vacuum pump system must meet NFPA99 design standards.  The minimum size is a duplex system where one vacuum pump can carry the entire load of the hospital and the 2nd pump (lag pump) then provides 100% backup. Vacuum serves a multitude of medical surgical operations such as chest drainage, gastro intestinal and pharyngeal/tracheal treatments. NFPA99 regulates the vacuum level at all hospitals shall be 19”HgG and the lowest allowable vacuum level at the furthest outlet form the source to be 12”HgG.  Capacity at all hospitals is given in SCFM and is generally defined as 70F air, 0% humidity and 14.7psia.

Vacuum pump manufacturers will use units of pump performance such as “HgG (inches mercury gauge) and Torr or mmHgA (millimeters of mercury absolute)   same measurement two different terms.   To convert 19”HgG to inches of mercury absolute (“HgA) 29.92”HgA – 19”HgG = 10.92”HgA. To convert from 10.92”HgA to say PSIA then 10.92”HgA/29.92”HgA x 14.7psia = 5.365 psia.

Because all vacuum pump curves are rated in ACFM from the manufacturer we need a way to convert from SCFM to ACFM so we can select a pump. In our example lets assume the hospital requires 25scfm @ 19”HgG, since air or gas under a partial vacuum is expanded our answer will always be a number larger than the 25scfm. Then 29.92”HgA/10.92”HgA x 25scfm = 68.5acfm @ 19”HgG.  Since medical vacuum shall always operate at 19”HgG then you may memorize the expansion factor of 29.92/10.92 = 2.74, this will always remain the same in medical surgical vacuum applications.

Controls on most medical vacuum pump systems are simply load/no-load. Medical vacuum controls most found today include load/No-Load, On/Off or VFD, rarely does any vacuum pump system use a modulated inlet valve. Typical vacuum pump will be single stage, standard materials of construction, common Hp size for a single pump will be anywhere from 5Hp to 40Hp range.

Liquid ring medical vacuum pump systems offer the greatest reliability and durability of any other type of mechanical vacuum pump and feature lowest noise level, a 40 year pump life, can compress up to ¼” soft solids, cool discharge temperatures and minimal maintenance. Water sealed liquid ring vacuum pumps offer the greatest safety and protection when considering WAG compression. Be cautions when considering technologies such as Claw vacuum pumps, especially for higher elevations as these machines are limited in maximum achievable vacuum levels (24”HgG max) and may not meet the NFPA 99 partial vacuum level (19”HgG) requirement. Other issues that should be considered with the Claw technology include high discharge temperatures (300F>) 3600rpm operations speed creates loud noise levels, and the inability of labyrinth seals to provide a 100% seal between the gear box and pumping chamber. Since claw technology does not include any type of clean up equipment on the pumps discharge it is possible to exhaust hot oil vapor directly into the discharge pipe.

Going Green

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“Green engineering” and “green design” are good sounding buzz words, but what do they really mean? According to the US Environmental Protection Agency, “going green” is defined as:

Green engineering is the design, commercialization, and use of processes and products, which are feasible and economical while minimizing 1) generation of pollution at the source and 2) risk to human health and the environment. Green engineering embraces the concept that decisions to protect human health and the environment can have the greatest impact and cost effectiveness when applied early to the design and development phase of a process or product.

Principles of Green Engineering*

  1. Engineer processes and products holistically, use systems analysis, and integrate environmental impact assessment tools.
  2. Conserve and improve natural ecosystems while protecting human health and well-being.
  3. Use life-cycle thinking in all engineering activities.
  4. Ensure that all material and energy inputs and outputs are as inherently safe and benign as possible.
  5. Minimize depletion of natural resources.
  6. Strive to prevent waste.
  7. Develop and apply engineering solutions, while being cognizant of local geography, aspirations, and cultures.
  8. Create engineering solutions beyond current or dominant technologies; improve, innovate, and invent (technologies) to achieve sustainability.
  9. Actively engage communities and stakeholders in development of engineering solutions.

*as developed by more than 65 engineers and scientists at the Green Engineering: Defining the Principles Conference, held in Sandestin, Florida in May of 2003. The preliminary principles forged at this multidisciplinary conference are intended for engineers to use as a guidance in the design or redesign of products and processes within the constraints dictated by business, government and society such as cost, safety, performance and environmental impact.

Facilities are constantly looking at ways to reduce cost and minimize waste, while at the same time trying to increase their equipment productivity and “go green”.  This is often easier said than done; however, the Powerex Scroll systems can do just that.  Utilizing multiple compressors with a completely oil-less design, our systems do not add contaminants to the air stream, there is no oil to change, and electrial consumption is minimized.  The heart of the system is the proven technology of the scroll compressor.  Quiet, efficient, and completely oil-less, the scroll compressor will provide reliable, clean compressed air for years to come.  By utilizing multiple compressors within one system, energy consumption is reduced.  This is achieved by powering the horsepower required based on demand – “staging” one compressor at a time as needed rather than turning on one large compressor for low air requirements.  Our systems automatically cycle through each compressor so wear is kept equal.

How To Wear Soft Foam Earplugs

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To get the best protection from your soft foam earplugs, remember to roll, pull, and hold when putting them in. Use clean hands to keep from getting dirt and germs into your ears!

1. Roll the earplug up into a small, thin "snake" with your fingers. You can use one or both hands

2. Pull the top of your ear up and back with your opposite hand to straighten out your ear canal. The rolled-up earplug should slide right in.

3. Hold the earplug in with your finger. Count to 20 or 30 out loud while waiting for the plug to expand and fill the ear canal. Your voice will sound muffled when the plug has made a good seal.

Check the fit when you're all done. Most of the foam body of the earplug should be within the ear canal. Try cupping your hands tightly over your ears. If sounds are much more muffled with your hands in place, the earplug may not be sealing properly. Take the earplug out and try again.

Infinity Quick-Fit Compressed Air Piping

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Infinity Quick-Fit has been specifically designed with many industries in mind. From simple home garage users to hi-tech machine builders and conveyor manufactures, Quick-Fit meets every need. The unique features of Quick_fit are its light weight marine grade aluminum tubing which will never corrode and its solid brass nickel plated fittings.

Installation of Quick-Fit is literally seconds and requires nothing more than a simple tube cutter and deburring tool for even the most complex installation. Cut, deburr and push together! Quick-Fit is in a master class of its own, the highest quality, the most durable and all at an affordable cost.

Optimizing Pumps & Systems

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Key Points

  • Equalize flow over production cycle using holding tanks.
  • Install parallel systems for highly variable load, or install a larger pump with speed controls.
  • Variable frequency drives (VFDs) allow pumps to operate at near top efficiency.

Today's business environment of globalization, increased competition and expanding regulations has forced many businesses to cut operating costs. While investment in cost-saving software and other technology has been significant, little attention has been paid to the continued use of outdated, inefficient motors. Pump systems, in particular, offer opportunities for optimizing production processes in a wide variety of industrial and commercial enterprises. Many proven strategies exist for optimizing pump system performance. The range of potential energy savings can be 20%–50%.

Optimizing Pumps and Pump-Systems

The U.S. Department of Energy’s Motor Challenge Program highlights a number of specific energy-efficiency measures for pump systems. These are listed in the table below, along with energy savings estimates.

Reduce Overall System Requirements (do not assume requirements are fixed).

  • Equalize flow over production cycle using holding tanks (10%–20% savings).
  • Eliminate bypass loops and other unnecessary flows (10%–20% savings).
  • Reduce "safety margins" in design system capacity (5%–10% savings).

Match Pump Size to Load.

  • Install parallel systems for highly variable load, or install a larger pump with speed controls (10%–50% savings).
  • Reduce pump size to better fit load (pumps are routinely oversized by 15%–25%).
  • The Hydraulic Institute recommends using two or more smaller pumps instead of one larger pump, so that excess pump capacity can be turned off.

Reduce/Control Pump Speed.

  • Reduce speed for fixed loads—trim impeller, lower gear ratio.
    • 82% of pumps have no load modulation.
    • Studies cite savings of 75% in food processing.
  • Replace throttling valves with speed controls to meet variable loads.
    • Adjustable Speed Drive installations show savings of 30%–80%. These savings only apply to circulating pump systems (not systems with static heads).

Improve Pump Components.

  • Replace typical pumps with the most efficient model, or one with an efficient operating point better suited to the operating flows.
    • 16% of pumps are older than 20 years old.
    • The problem is not the age of the pump, but that the process has changed over time.
    • 10%–25% savings.

Operation and Maintenance.

  • Replace worn impellers, especially in semi-solid applications. Inspect and repair bearings, lip seals, packing and other seals.
    • Pump efficiency degrades from 1%–6 % for impellers less than maximum diameter, and with increased wear-ring clearance.
    • The Hydraulic Institute recommends maintaining pumps and all system components in virtually new condition to avoid efficiency loss.
    • Use pumps operating as turbines to recover pressure energy that would otherwise be wasted.

Friction Losses

In the fluid system, unnecessary friction can increase energy use. In a system that is already designed and built, controlling friction caused by pipe size or roughness is nearly impossible. However, operators can improve friction inefficiencies caused by piping components, unnecessary flow paths and high flow rates. Throttle valves, in particular, are associated with friction losses. Measurements can be taken to determine efficiency loss through friction. Loss coefficients are published by the Hydraulic Institute or by valve manufacturers.

Variable Frequency Drives

Traditionally, control valves were used to control fluid flow in pumping systems. Increasingly, variable frequency drives (VFDs) are being used, especially with intelligent drives. VFDs allow pumps to operate at near top efficiency and protect the system from mechanical damage when they do not. With VFDs, pumps can run at slower speeds with trimmed impellers, thereby increasing system reliability and decreasing failure rates. In new applications, VFDs are normally less expensive to purchase and install than control valves. The reduced energy and maintenance costs associated with VFDs make them a good fit for retrofits in older pumps systems as well.

Other Savings Opportunities

In addition to the improvements mentioned above, other measures for reducing pump system components include adjusting the system flow paths, trimming the pump impeller, and adding a gear reducer and a two-speed motor to the existing pump system.

The Pumping System Assessment Tool (PSAT), offered by the U.S. Department of Energy’s Office of Industrial Technology, helps to assess the efficiency of pumping system operations. PSAT uses achievable pump performance data from Hydraulic Institute standards and motor performance data from the MotorMaster+ database to calculate potential energy and associated cost savings. The PSAT software is offered free of charge.

The Power of Vacuum Condensers

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Process condensers and pre-condensers should be considered when large condensable loads are indentified in a vacuum pumping system. Imagine one cubic foot of water being heated; turning into steam that one cubic foot of water now occupies 1700cu/ft of space. The proper use of condensers will allow the use of a smaller vacuum pump, reducing total energy and capital costs. Condensers will also recover valuable process materials. Reducing the condensable pump load to a liquid ring vacuum pump translates into a smaller heat exchanger; less temperature rise due to condensation inside the liquid ring means a deeper vacuum level and higher capacity pump.  Reducing the condensable load to oil sealed or dry vacuum pump (pumps with a low tolerance to vapor loads) will mean the difference between consistent catastrophic pump failures and normal pump operation.

The use of a condenser is not always technically possible. If the dew point of a gas stream is less than the available cooling medium temperature, the condenser can’t be used to remove process vapors. In a direct contact condenser, a device that uses direct contact of the cooling medium to condense the vapor load, condensing will not be possible at pressures below the vapor pressure of the cooling medium. If the use of a condenser proves possible the question becomes one of economics. Will the potential of reduced capital and operating costs for the vacuum pump offset the new costs of the condenser, associated components, and utilities.  Valuable product recovery, an increase in pumping system reliability, smaller vacuum pump and related components, reduced operating costs and a number of other factors must be considered.

The proper sizing of both the condenser and the vacuum pump depends on an accurate estimation of the condensable vapor load.  Process gasses from many vacuum applications will contain 95 to 100 percent condensable vapors. When process condensers are not in use, the vapor load entering the pre-condenser or the vacuum pump can be considered large. This load should be treated as evaporated vapor because the flow rate of this type of stream is directly related to the evaporation rate in the process vessel.

Air leaking or intentional release of non-condensables into a process vacuum system will become saturated with vapors as they contact the liquid process stream. Condensable vapors that saturate non-condensable gases are called “vapors of saturation”. If these vapors are present they must also be accounted for in order to calculate the load to the condenser or vacuum pump.

In the ideal process conditions the condenser can be the most energy efficient, cost effective vacuum pump ever developed.
 
Example – Process Condenser using Simple Water

Customer requirements:

P1 - 760mm
P2 - 125mm
Pd - 760mm
Tg - 135f.
Tw - 65F.
Condensable pump load: 500lbs/hr water vapor
Non-condensable pump load: 50lbs/hr air

Step 1: Determine pump size without the implementation of a process condenser.

Step 1a. Determine volumetric requirement by using the ideal gas law PV=nRT

V= (n)(R)( 1/P)(T)

V= 1,368acfm @ 125mm

The type of mechanical pump selected must be a liquid ring vacuum pump due to the large condensable pump load.  The volumetric requirement calculated would indicate an initial pump size using a 125Hp motor. After performing a mass balance on the discharge side of the liquid ring it was found that the temperature rise exceeds 20f. and the next larger pump size was selected with a greater service liquid flow. The pump size now requires a 150Hp motor and carries an estimated system capital cost of $75,000.00.

Step 2: Determine pump size when implementing a process condenser.

Step 2a. Determine Process conditions at the inlet of the condenser

Inlet process conditions: P2 – 125mm
                                    Tg – 135f
                                         Condensable pump load: 500lbs/hr water vapor
                                         Non-condensable pump load: 50lbs/hr air

Step 3: Determine new process conditions at the vacuum pump inlet

P1 - 760mm
P2 - 120mm
Pd - 760mm
Tg - 80f.
Tw - 65F.
Condensable pump load: To be determined
Noncondensable pump load: 50lbs/hr air

Step 4: Determine amount of water in the air by using Dalton’s law of partial pressures. Assume 60f cooling water into the condenser and 70f out (70f +10f approach = 80f gas temp)

Wi = Wair Mi/29 (Xi Yi Poi/P-pc )  
Where Wi = mass flow rate of vapor
Wair  = mass flow rate of air
Mi  = Molecular weight of vapor

Wi = 10lbs/hr water vapor

The power of condensing becomes clear as we are able to reduce the 500lbs/hr of water vapor to 10lbs/hr.

Step 5: Determine volumetric requirement by using the ideal gas law PV=nRT

V = 95.5acfm @ 120mm

The volumetric requirement calculated would indicate an initial pump size using a 7.5Hp motor and carries an estimated system capital cost of $5,500.00.

Estimated capital cost of pump alone: $75,000.00
Estimated capital cost of pump when using process condenser: $5500.00

Estimated Vacuum Pump Capital Savings…$69,500.00

The example using simple water is very common on applications such as Uranium drying where very large condensable loads are encountered and the implementation of a process condenser saves thousands of dollars in capital and operating costs.