Pump Construction Types
Bronze-Fitted Pumps:
- Cast iron body, brass impeller, brass seal components
- Use for: Closed heating/chilled water systems, low-temperature fresh water
All-Bronze Pumps:
- All wetted parts are bronze
- Use for: Higher temperature fresh water, domestic hot water, hot process water
Pump Impeller Types
| Type | Description | Application |
|---|---|---|
| Single Suction | Fluid enters one side of impeller | Standard applications |
| Double Suction | Fluid enters both sides | High-flow applications, reduced NPSH requirement |
| Closed | Shroud encloses pump vanes | Clean fluid systems — highest efficiency |
| Semi-Open | No inlet shroud | Moderate particles in fluid |
| Open | No shroud | Large particles — sewage, sludge |
Pump Body Types
Horizontal Split Case: Split along horizontal centerline. Disassemble by removing top half. Impeller between bearings. Requires two seals. Usually double suction. Suction and discharge in straight-line configuration.
Vertical Split Case: Single-piece body with cover plate. Shaft through seal and bearing in cover. Impeller on shaft end. Suction at right angle to discharge.
Pump Mounting Methods
| Method | Description | Pros |
|---|---|---|
| Base Mount — Long Coupled | Pump coupled to base-mount motor | Motor removable without disturbing pump; standard motors |
| Base Mount — Close Coupled | Impeller on motor shaft | More compact; no separate pump mounting needed |
| Line Mount | Mounted to and supported by system piping | Very compact; usually for low-flow |
Affinity Laws for Pumps
The pump affinity laws are analogous to fan laws:
Variable Speed, Constant Impeller:
| Parameter | Relationship |
|---|---|
| Flow | New Speed / Old Speed |
| Head | (New Speed / Old Speed)² |
| BHP | (New Speed / Old Speed)³ |
Variable Impeller, Constant Speed:
| Parameter | Relationship |
|---|---|
| Flow | New Diameter / Old Diameter |
| Head | (New Diameter / Old Diameter)² |
| BHP | (New Diameter / Old Diameter)³ |
Variable Specific Gravity:
| Parameter | Relationship |
|---|---|
| BHP | New SG / Old SG |
Common Pump Formulas
Head:
H = PSI × 2.31 / SG (feet)Output Power:
Po = Qv × H × SG / 3,960 (horsepower)Shaft Power:
Ps = Qv × H × SG / (39.6 × Ep) (horsepower)Input Power:
Pi = Ps × 74.6 / Em (kilowatts)Pump Horsepower:
HP = GPM × Feet Head × Specific Gravity / (3,960 × % Efficiency)Typical Pump Efficiencies:
| Pump Size | Efficiency Range |
|---|---|
| 1/12 to 1/2 HP (single suction) | 40% – 55% |
| 3/4 to 2 HP | 45% – 60% |
| 3 to 10 HP | 50% – 65% |
| 20 to 50 HP (double suction) | 60% – 80% |
Water Flow and Piping
Pressure drop varies as the square of flow:
h₂/h₁ = (Q₂/Q₁)²Water velocity in a pipe:
v = GPM × 0.41 / d²
Where: v = velocity (ft/sec), d = inside diameter (inches)Quiet Water Flow Limits (6 fps maximum):
| Pipe Size | Max Quiet Flow (GPM) |
|---|---|
| 1/2" | 1.5 |
| 3/4" | 4 |
| 1" | 8 |
| 1-1/4" | 14 |
| 1-1/2" | 22 |
| 2" | 44 |
| 2-1/2" | 75 |
| 3" | 120 |
| 4" | 240 |
Pumping System Troubleshooting Guide
Symptom: Pump or System Noise
| Possible Cause | Action |
|---|---|
| Shaft misalignment | Check and realign |
| Worn coupling | Replace and realign |
| Worn bearings | Replace, check lubrication schedule, realign |
| Improper foundation | Check bolting/grouting, check for shifting from pipe expansion |
| Pipe vibration from expansion | Inspect/add hangers and expansion provisions |
| Water velocity too high | Check actual performance vs. specified; reduce impeller diameter |
| Operating beyond curve end | Reduce impeller diameter |
| Entrained air / low suction pressure | Check expansion tank connection; check for vortex; verify NPSH |
Symptom: Inadequate or No Circulation
| Possible Cause | Action |
|---|---|
| Running backward (3-phase) | Reverse any two motor leads |
| Broken coupling | Replace and realign |
| Improper motor speed | Check nameplate wiring and voltage |
| Pump/impeller too small | Check selection against requirements |
| Clogged strainer | Inspect and clean screen |
| System not filled | Check PRV fill valve; vent terminal units and high points |
| Valves improperly set | Check balance and isolation valve settings |
| Air-bound system | Vent piping; check expansion tank connection; review air elimination |
| Air entrainment | Check suction inlet conditions for vortex |
| Low available NPSH | Check NPSH required; inspect strainers; check pipe sizing and water temperature |
Typical Heat Transfer Coefficients (U-Factors)
| Application | Controlling Fluid | U Free Convection | U Forced Convection |
|---|---|---|---|
| Air — flat plates | Gas to gas | 0.6 – 2 | 2 – 6 |
| Air — bare pipes | Steam to air | 1 – 2 | 2 – 10 |
| Air — fin coil | Air to water | 1 – 3 | 2 – 10 |
| Oil preheater | Liquid to liquid | 5 – 10 | 20 – 50 |
| Oil preheater | Steam to liquid | 10 – 30 | 25 – 60 |
| Water — shell & tube | Water to water | — | 150 – 300 |
| Water — shell & tube | Condensing vapor to water | — | 150 – 800 |
| Brine — DX chiller | Brine to R12/R22/NH3 | — | 60 – 140 |
| Water — DX shell & tube | Water to R12/R22/NH3 | — | 130 – 190 |
Units: BTU/(hr·ft²·°F). Values for commercially clean equipment. Liquid velocities 3 ft/sec or higher.
Cooling Tower Ratings
| Hot Water (°F) | Cold Water (°F) | Wet Bulb (°F) | Capacity Factor |
|---|---|---|---|
| 90 | 80 | 70 | 0.85 |
| 92 | 82 | 70 | 1.00 |
| 95 | 85 | 70 | 1.24 |
| 90 | 80 | 72 | 0.74 |
| 92 | 82 | 72 | 0.88 |
| 95 | 85 | 74 | 1.00 |
| 95 | 85 | 76 | 0.88 |
| 95 | 85 | 78 | 0.75 |
| 95 | 85 | 80 | 0.62 |
Key Definitions:
- Range = Hot Water Temperature − Cold Water Temperature
- Approach = Cold Water Temperature − Wet Bulb Temperature
- Heat Rejection Ratio: Based on 1.25 (15,000 BTU/hr per ton)
Cooling Tower Bleed: Evaporation concentrates dissolved solids. A 1% bleed of circulation rate = 2 concentrations of original solids. A 0.5% bleed = 3 concentrations.
Formulas and Conversion Factors — Your Pocket Calculator
Electrical Formulas
Ohm's Law:
Ohms = Volts / Amperes (R = E/I)
Amperes = Volts / Ohms (I = E/R)
Volts = Amperes × Ohms (E = I×R)Three-Phase AC Power:
Kilowatts = V × A × PF × 1.732 / 1,000
Amperes = 746 × HP / (1.732 × V × Eff × PF)
Horsepower = V × A × 1.732 × Eff × PF / 746Single-Phase AC Power:
Kilowatts = V × A × PF / 1,000
Amperes = 746 × HP / (V × Eff × PF)
Horsepower = V × A × Eff × PF / 746Motor Application Formulas
Torque (lb-ft) = HP × 5,250 / RPM
HP = Torque (lb-ft) × RPM / 5,250
Synchronous RPM = Hz × 120 / Poles
% Slip = (Synch RPM − Full Load RPM) / Synch RPM × 100Time for Motor to Reach Operating Speed:
Seconds = WK² × Speed Change / (308 × Avg. Accelerating Torque)
Where:
Avg. Accelerating Torque = [(FLT + BDT)/2 + BDT + LRT] / 3
WK² = Inertia of Rotor + Inertia of Load (lb-ft²)Fan and Blower Formulas
Tip Speed (ft/sec) = D(in) × RPM × π / 720
BHP = CFM × PSF / (33,000 × Efficiency)
BHP = CFM × PIW / (6,344 × Efficiency)
BHP = CFM × PSI / (229 × Efficiency)Vibration Formulas
D = 0.318 × (V/f) D = Displacement (inches peak-to-peak)
V = π × f × D V = Velocity (inches/sec peak)
A = 0.051 × f² × D A = Acceleration (g's peak)
A = 0.016 × f × V f = Frequency (cycles/sec)Temperature Conversion
°F = (°C × 9/5) + 32
°C = (°F − 32) × 5/9Pressure Conversions
1 foot of water = 0.433 PSI
1 PSI = 2.309 feet of water
1 inch of water = 248.8 Pa
1 PSI = 6.895 kPaEssential Conversion Factors
| Multiply | By | To Get |
|---|---|---|
| BTU/hr | 0.293 | Watts |
| HP | 746 | Watts |
| kW | 1.341 | HP |
| CFM | 0.4719 | Liters/sec |
| GPM | 0.0631 | Liters/sec |
| ft/min | 0.00508 | m/s |
| PSI | 6.895 | kPa |
| in. WG | 248.8 | Pa |
| BTU/hr·ft²·°F (U-value) | 5.678 | W/(m²·K) |
| ft²·hr·°F/BTU (R-value) | 0.176 | m²·K/W |
| tons of refrigeration | 3.517 | kW |
| feet | 0.3048 | meters |
| inches | 25.4 | millimeters |
| gallons (US) | 3.785 | liters |
| cubic feet | 0.02832 | cubic meters |
| pounds (mass) | 0.4536 | kilograms |
| lb/ft³ | 16.0 | kg/m³ |
Key engineering insight
Six months after the practitioner first walked into the practitioner's mechanical room, the building was running as designed — actually, better than designed. Every system had been recalculated for actual conditions, every installation issue had been corrected, and every comfort complaint had been resolved.
But the real transformation wasn't in the building. It was in the practitioner.
"I used to think being a good mechanical designer meant getting the calculations right," he told the practitioner during their final walkthrough. "Now I know it means getting the conditions right — altitude, temperature, installation details, prevailing winds, noise criteria, vibration isolation, water chemistry, expansion tank placement — and THEN getting the calculations right."
the practitioner smiled. "Welcome to field engineering. The textbook is where you start. The field is where you finish."
Here's what the practitioner now does differently on every project:
- Visits the site before designing. He checks altitude, prevailing winds, nearby odor sources, and available mechanical room space.
- Corrects all fan and motor selections for actual air density — not standard conditions.
- Specifies installation details on drawings — minimum straight duct lengths, screen types, damper types, and vibration isolation requirements.
- Includes a commissioning specification that requires field verification of fan rotation, motor voltage, airflow rates, water flow rates, and sound levels.
- Designs for the worst case — highest summer temperature, lowest winter temperature, maximum occupancy, dirtiest filter condition — and verifies the system still works at partial load.
- Keeps a field reference with all the tables, formulas, and troubleshooting guides from this handbook. Because when you're on a rooftop at 2 AM, you don't have time to look things up in a textbook.
What the practitioner Learned
the practitioner's building is now fully occupied. The tenants are comfortable. The restaurant smell stays in the restaurant. The luxury apartments are quiet. The motors don't trip.
He tells his contractor friends: "Hire the designer who asks about the altitude. If they don't ask, find someone who does."
Your Next Move
You've just absorbed the equivalent of decades of field experience compressed into one guide. But knowledge without action is just trivia.
Here's what to do right now:
Bookmark this guide. You'll need it on your next project — probably sooner than you think.
Check your current project. Are you designing for actual air density, or are you assuming sea level and 70°F? Are your fan installation details specified on the drawings? Is your expansion tank connected to the pump suction?
Build your own field reference. Print or save the tables that are most relevant to your work — air density factors, motor full load currents, ventilation rates, heat gain from occupants, duct velocity guidelines, pump troubleshooting checklist.
Walk a job site before your next design. Spend one hour on the roof, in the mechanical room, and at the location of every major piece of equipment. You'll catch problems on paper that would have cost thousands to fix in the field.
Find your the practitioner. Every designer needs a field mentor — someone who has seen the consequences of every design shortcut and can tell you which ones matter and which ones don't.
What's the biggest HVAC design mistake you've encountered in the field? Share your story — every lesson learned is a lesson earned.
This comprehensive guide was developed from the "Handbook for the Mechanical Designer" (Second Edition), originally published by the equipment supplier, Springfield, MO — with deep gratitude to the many fine mechanical designers in our industry who contributed their hard-won field knowledge to this essential reference.
All technical data, formulas, tables, and standards referenced herein are adapted from ASHRAE Handbooks, AMCA Standards, the National Electrical Code®, and other authoritative industry sources as noted throughout. Always verify with the latest edition of applicable codes and standards for your jurisdiction.
© Content Transformation for Educational Purposes. Technical data sourced from industry-standard references. All currencies and measurements intentionally kept in universal engineering units applicable globally. No time-bound pricing or region-specific regulations referenced to ensure lasting applicability.