What you need to gather first

You need data for three streams: motive liquid, suction liquid, and outlet conditions. The catalog lists these exact inputs.

Motive liquid (powers the eductor)

Available motive pressure (flowing)
Available motive flow (if limited)
Specific gravity, viscosity, temperature
Vapor pressure at temperature

Suction liquid (the one you want to pump)

Required suction flow (GPM)
Lift/head from suction liquid surface to eductor centerline
Specific gravity, viscosity, temperature
Vapor pressure at temperature

Outlet (where it discharges)

Outlet head or backpressure
Include elevation + downstream restrictions/valves
If using outlet head, you’ll need outlet liquid specific gravity

Step-by-step sizing (liquid motive pumping liquid)

Our catalog provides the sizing procedure in 5 steps using the performance tables and a “Sizing Factor” approach based on the 1-1/2″ standard unit.

Step 1 — Determine suction “severity”: use suction lift or (better) NPSH

Basic method: Find suction lift/head (H_s) that is equal to or greater than your required lift. If you’re between table values, interpolate.

Better method (recommended): Use the catalog’s NPSH calculation to correct for:

liquid temperature (vapor pressure),
specific gravity,
suction piping friction losses.

NPSH formula (from the catalog):

Where:

(P_s) = suction vessel pressure (psia) (14.7 psia at sea level if vented)
(P_{vp}) = vapor pressure at operating temp
(S_g) = specific gravity of liquid pumped
(H_s) = vertical feet above/below eductor centerline (negative if liquid is below)
(H_f) = suction piping friction loss at full flow (ft of liquid)

Important warning: Calculate NPSH for both suction and motive liquids because either one can flash in the suction chamber if vapor pressure is high—this can cause reduced/zero pumping or even motive fluid exiting the suction port.

Step 2 — Determine outlet head (H_o) (include friction with combined flow)

Pick outlet head (H_o) equal to or greater than actual. Include friction losses in the outlet line calculated using the combined flow (motive + suction).

Also: outlet line should be as large or larger than the eductor outlet connection.

Step 3 — Use the performance tables to find tabulated suction flow and compute Sizing Factor

From the table:

choose motive pressure (P_m) closest to or lower than your actual motive pressure.
read the Tabulated Suction Flow for each model (SL/ML/HL) at your (H_s), (H_o), and (P_m).

Then compute Desired Sizing Factor (S.F.) (catalog calls it S.F. / S.P. depending on section):

Select a physical unit size whose Tabulated S.F. is ≥ your desired S.F. (the catalog provides a sizing factor table by unit size for this scaling approach).

Step 4 — Calculate actual motive flow (and check it against what you can supply)

You will need to scale both motive and suction flows by the tabulated sizing factor you selected.

In practice for liquid-motive units:

Then verify:

your supply can deliver (Q_m) at the flowing pressure you assumed.

Step 5 — Pick the best model (SL vs ML vs HL) and handle turndown

Select the model that best matches your desired motive-to-suction ratio and constraints.

If you need turndown > 35%, the catalog recommends using two or more eductors in parallel and staging them.

For many pumping applications, pick the unit that gives required suction flow while using the least motive flow.
For dilution applications, motive may be intentionally high and suction throttled; as a rule, HL is often preferred for dilution.

Corrections when the fluids are not water

The performance tables are based on water (SG 1.0, ~1 cP) at ~68°F, so you must correct for different fluids.

A) Viscosity guidance

< ~100 cP: negligible effect
Up to ~500 cP: small corrections
500 cP: consult factory/rep; still possible with calculated adjustments

B) Motive flow adjustment for specific gravity

To adjust motive flow from table for motive liquid SG:

C) Suction side adjustment

Best method: use NPSH calculation (especially if suction liquid temp > 100°F).
Rough estimate: multiply suction lift by suction liquid SG (but the catalog warns that higher temps require NPSH).

D) Outlet adjustment if discharging to elevation

If outlet is specified as feet of head to an elevated surface, adjust by outlet SG:

If discharge is controlled by a regulator/valve in pressure terms, no adjustment is required.

Quick “common mistakes” this guide avoids

Ignoring outlet friction losses at combined flow (Qm + Qs)
Using lift without correcting for temperature/vapor pressure (NPSH)
Not checking motive liquid flashing risk (must calculate NPSH for motive too)
Expecting big turndown from one eductor instead of staging multiple units

Unified Liquid-Motive Eductor Performance Map

(Derived from liquid-motive tables – standard basis: 1½″ eductor, water @ ~68°F)

1️⃣ Performance Envelope (all models)

These are absolute operating limits from the catalog:

Parameter	Liquid-Motive (SL / ML / HL)
Motive pressure	15 – 250 psig
Maximum suction lift	-27 ft
Minimum required NPSH	3 ft
Fluids	Water or other liquids
Reference liquid	Water, SG = 1.0, 68°F

This envelope defines what any size eductor in this family can do.

2️⃣ Model Behavior (what the three curves really mean)

The performance tables are really three families of curves:

Model	Pressure Recovery	Flow Behavior	Typical Use
SL	10–15%	Low motive flow, low suction	High lift, low dilution
ML	30–35%	Balanced motive/suction	General pumping
HL	40–50%	High motive, high suction	Dilution, aggressive entrainment

So the tables are actually three surfaces:

Suction Flow = f( Motive Pressure, Suction Lift, Outlet Head )

for each model.

3️⃣ Unified Table Logic

Inputs:
• Suction Lift (Hs)
• Outlet Head (Ho)
• Motive Pressure (Pm)

Output:
• Tabulated Suction Flow (Qs) for each model (SL, ML, HL)
• Tabulated Motive Flow (Qm)

Those flows are always for a 1½″ reference eductor.

4️⃣ One Consolidated Performance Graphic

                           LIQUID EDUCTOR PERFORMANCE SURFACE
                   (Standard 1½" Unit – Water @ 68°F)

                    ↑ Suction Flow (Qs)
                    |
                    |             HL
                    |            /
                    |           /
                    |          /
                    |         /     ML
                    |        /
                    |       /
                    |      /    SL
                    |_____/________________________→ Motive Pressure (Pm)
                         ↑
                         Suction Lift (Hs) increases downward
                         Outlet Head (Ho) increases rightward

As:

Motive pressure increases → Qs increases
Suction lift increases → Qs decreases
Outlet head increases → Qs decreases
HL > ML > SL in suction capacity at same conditions

5️⃣ How Size Changes Everything (Sizing Factor Map)

The catalog makes all tables scalable via Sizing Factor (S.F.)

Actual Suction Flow = Tabulated Suction Flow × S.F.
Actual Motive Flow  = Tabulated Motive Flow × S.F.

Eductor Size	S.F. (Typical)
¾″	~0.25
1″	~0.40
1¼″	~0.60
1½″	1.00 (reference)
2″	~1.6
3″	~3.5
4″	~6
6″	~15

(This is why our catalog only publishes tables for one size.)

6️⃣ What the tables are REALLY used for

The catalog’s procedure collapses all tables into this single formula:

Then choose a unit whose Tabulated S.F. ≥ Desired S.F.

That’s the whole selection logic.

7️⃣ What changes the table values

The tables are valid only for water @ ~70°F.

They must be corrected by:

Variable	Effect
Higher temperature	Lowers NPSH → reduces lift
Higher vapor pressure	Reduces allowable lift
Higher SG	Increases head requirements
Viscosity >100 cP	Reduces flow
Long suction piping	Reduces NPSH
Long discharge piping	Increases Ho

Which is why you will need NPSH correction before using the tables.

“Given motive pressure, suction lift and outlet head, each model (SL, ML, HL) produces a suction flow. Scale that by size. Correct for NPSH.”