1. What the Dri-Prime actually is

Godwin's Dri-Prime is an automatic, self-priming centrifugal pump. The "Dri-Prime" name refers to the priming method: a compressed-air-driven venturi evacuates air from the suction hose and pump body until liquid rises into the casing, at which point pumping begins. A non-return ball seals the discharge during priming so the pump doesn't draw air backward.

The two practical consequences for sizing are these: the pump primes from dry to 28 ft of suction lift, and it can run dry indefinitely because the mechanical seal sits in an oil/glycol bath that dissipates heat through the casing rather than relying on the pumped fluid for cooling. That's why Dri-Primes dominate construction dewatering — they handle intermittent suction, fluctuating water levels, and operator-unattended cycling without burning seals.

2. The four numbers you need before you call

Whether you're calling us for a quote, calling Xylem rental, or specifying for a bid, every Dri-Prime selection conversation starts with the same four data points. If you don't have all four, the answer you get is a guess.

3. How to calculate Total Dynamic Head (TDH)

TDH is the total resistance the pump has to overcome to move your flow from suction to discharge. It's the y-axis of every Godwin performance curve. The basic equation:

For 95% of construction dewatering jobs, you can ignore velocity head (it's typically under 2 ft) and pressure head (atmospheric discharge to a pond, ditch, or sewer). That leaves:

Static head — what to actually measure

Static head is the vertical distance, measured in feet, from the water surface elevation at the source to the discharge elevation. If you're pulling water out of a 12 ft deep trench and discharging into a sediment tank 8 ft above grade, your static head is roughly 20 ft. The horizontal distance doesn't enter static head — that comes into friction.

Friction head — the part contractors usually underestimate

Friction loss depends on flow rate, hose ID, hose length, fittings, and fluid viscosity. For clean water at typical construction temperatures, the friction loss per 100 ft of layflat or hard-suction hose follows these approximate values:

These are approximate Hazen-Williams values for clean water with C=120. For solids-laden discharge (sewage, sludge, sediment-loaded site water), increase friction loss by 20%–40%. For long runs, add elbow, valve, and fitting equivalent lengths.

4. Sizing example — typical Houston-area trench dewatering job

Walk through a realistic scenario to see how the numbers play out:

Step 1: Required flow — Estimated 600 GPM at peak. Round up to 750 GPM for design margin; you'd rather have unused capacity than be overrun. Real groundwater inflow estimates are notoriously soft, and the cost of being too small is a flooded excavation.

Step 2: Suction lift — Pump at grade, water at 14 ft depth = 14 ft suction lift. Well under the 28 ft limit, so a Dri-Prime is appropriate.

Step 3: Static head — Source water 14 ft below grade, discharge at grade = 14 ft of static head, lifting the water from the trench bottom to grade level.

Step 4: Friction head — At 750 GPM design flow with a 6 in discharge hose over 400 ft, friction is approximately 4 ft per 100 ft × 4 = 16 ft. Add another 4 ft for the 12 ft suction hose and fittings. Total friction head ≈ 20 ft.

Step 5: Total Dynamic Head — Static (14) + Friction (20) = 34 ft TDH at 750 GPM design flow.

Step 6: Model selection — Looking at the CD series performance: a CD100M handles 100–750 GPM with a max TDH of 125 ft. Easily covers 750 GPM at 34 ft TDH with comfortable margin. A CD150M (700–2,080 GPM, max TDH 160 ft) would be oversized; you'd be running it at the low end of its curve, which is wasteful.

Answer: CD100M diesel-drive Dri-Prime. 4 in by 4 in branch size, fits your hose plan, sized correctly without overspending.

5. The CD series — Diesel Dri-Prime spec reference

The CD (Construction Dewatering) series is Godwin's most-used Dri-Prime line. High-volume, medium-head, large solids handling. These are the trailers and skids you see on virtually every major construction site doing groundwater control.

Source: Godwin Dri-Prime US product catalog. Electric-drive versions of these models are available with reduced max head (motor speed limits to 1,800 RPM vs 2,200–3,000 for diesel). Solids handling represents largest spherical solid that can pass.

6. When the CD isn't right — HL and NC series

HL series — high-head models

NC series — Flygt N-impeller models

7. Diesel vs Electric drive — what to pick when

Every CD, HL, and NC series Dri-Prime is available in either diesel or electric drive. The choice depends on jobsite power, duration, and noise constraints.

8. Pre-engineered options worth knowing about

DBS — Dri-Prime Backup System

The DBS is a packaged automatic backup pump for lift stations and pump stations. Sits idle until the primary pump fails, then auto-starts and runs the bypass. Common spec for municipal lift station resilience. Available in CD or NC configurations matched to the station's design point.

Critically Silenced enclosure

Standard 14-gauge sheet metal (12-gauge for larger units) lined with polydamp acoustical material, critical-grade silenced muffler, silenced priming exhaust, isolated engine vibration. Rated approximately 69 dBA at 30 ft. Mandatory for night work in noise-restricted municipalities, residential neighborhoods, or near hospitals.

Pump end material upgrades

• Standard cast iron — clean water, normal site water, raw sewage. Most economical.
• 316 stainless steel — moderately corrosive fluids, brackish water, low pH process water.
• CD4MCu duplex stainless — high-pH or low-pH industrial fluids, chemical processing, mine water.
• Hard iron / high chrome — abrasive slurries, sand-laden water, sediment-heavy industrial process.

9. Why this matters for your project — and your bid

Sizing matters in two directions, and most contractors only think about one of them.

Undersizing is the obvious failure mode: pump can't keep up with inflow, excavation floods, schedule slips, crews stand idle, the GC is calling at 6 AM. Everyone understands this risk.

Oversizing is the quiet money-drain. A CD150M instead of a CD100M for a 750-GPM job means roughly 2.5x the rental cost, 2.5x the fuel burn, and a pump operating at the low-flow end of its curve where efficiency is poor and the bearings see harder service. Over a 90-day job, the difference between a right-sized pump and a "just to be safe" oversized pump can easily exceed $30,000–50,000 in rental and fuel cost.

For purchased pumps (lift station backup, permanent installations, repeat dewatering work), oversizing is even worse — you carry the higher capital cost for 15+ years and burn extra power every hour the pump runs.

10. Common sizing questions