How to Size Liquid Motive Eductors for Pumping Liquids

Using Liquid Motives to Pump Liquid Suction Fluids
To determine the correct eductor for a specific application, follow the steps in this section, using the performance tables provided to achieve your desired results. (NOTE: All Jacoby-Tarbox eductor tables use the 1-1/2 inch unit as the standard, and eductors are sized using a Sizing Factor (S.E) based on this standard unit.)

*Step 1*
Find the suction lift* or head (Hs) that is equal to or greater than your desired lift. If your lift is between two of the lifts on the table, use an average of the two. You can also or use the calculated result from the NPSH formula found on page 5 of this manual. Using the NPSH number will correct for temperature variations and friction losses, resulting in a more accurate value.

*Step 2*
Find the outlet head** (Ho) equal to or greater than your actual outlet head. It is important to include friction losses into the desired outlet head. (Be certain that friction losses in the outlet line are calculated using the combined rate of both the motive and the suction flows.) It is important that the outlet line from the eductor be as large or larger than the outlet connection.

Step 3

Find the motive pressure (Pm)' Locate the motive pressure from the table that is closest to or lower than your actual motive pressure. The flow specified represents the Tabulated Suction Flow for each of the different models of eductors. To determine the size of eductor needed, first use the following formula to determine the Desired Sizing Factor (S.F.) Do this for each of the models.

Desired S.F. =	Desired Suction Flow
Desired S.F. =	Tabulated Suction Flow

If a standard unit is being used, pick the size unit that has a Tabulated S.E equal to or greater than the Desired S.F.
If an exact match is desired, consult your Jerguson/Jacoby-Tarbox representative.

Step 4

Calculate the amount of motive flow used by multiplying the Q," and Qs found in the tables by the Tabulated S.E obtained in Step 3. Do this for each of the models of eductors.

Step 5

Select the unit from Steps 1-4 that best meets the motive and suction parameters of the specific application. If a turndown ratio*** of greater than 35% is needed, then choose two or more eductors that have the correct turndown ratio and operate these units in parallel.

In some cases, the unit chosen will have the greatest suction flow while consuming as little motive fluid as possible. This is generally true for pumping applications. In other applications, such as the dilution of chemicals, the motive flow should be as high as possible: while the suction flow will be low. In this case, the motive flow should be matched to the desired motive flow and the suction port should be throttled to achieve the desired dilution rate. As a general rule in dilution applications, the HL is the best unit to choose.

In all cases, the correct unit is the one that matches your desired range of motive-to-suction flows the closest.

Correcting for Non-Water Fluid Specifications

The performance specifications for Jacoby-Tarbox eductor eductors are based on using water with a specific gravity of 1.0 and a viscosity of 1 Centipoise. Fluids with differing viscosities or specific gravities need to be corrected to water, to obtain accurate performance estimates.

Viscosity is the measure of the internal resistance of a fluid to flow. This should be taken into consideration in most pressure drop and flow calculations within a given system. When used with Jacoby-Tarbox eductor eductors, fluids with viscosities of less than 100 Cp. have a negligible effect. Viscosities of up to 500 Cp. can be used with only small corrections. For higher viscosities (applications above 500 Cp.), we suggest that you work with your trained representative or the applications personnel at the factory. Eductors can be used with viscosities over 500 Cp. with calculated adjustments. The effects of viscosity on the pressure drops in the line leading to the eductor must be calculated separately.

Specific gravity is the measure of the weight per volume of a liquid. The performance data for eductors is based on water having a specific gravity of 1.0; other specific gravities will require that adjustments be made to the performance table value of the eductors. See the topics that follow for specifics on how to make these adjustments.

Motive Flow Adjustments

The motive flow is the amount of liquid used to power the eductor. To adjust the value from the performance table for specific gravity (Sg) of the motive fluid: Multiply the motive flow in the performance chart by the square root of(1/Sg).

Example: 50 GPM Tabulated Flow adjusted for a Specific Gravity of 1.3: 50 x(1/1.3) = 43.85 GPM Actual motive flow

Suction Flow Adjustments

The best way to adjust for the specific gravity or temperature effects of the suction fluid is to do the calculation for NPSH (see page 5 of this manual). If you desire a rough estimate of the specific gravity effect, multiply the suction lift by the specific gravity of the liquid. If the liquid temperature exceeds 100°F, you must use the NPSH calculation, or consult your representative or the factory.

Outlet Adjustments

The outlet pressure of the eductor must be adjusted for the specific gravity of the outlet liquid, particularly if the eductor is discharging to an elevated surface. If the outlet is being measured or controlled by a pressure regulator or valve, no adjustment is required. To calculate the actual outlet pressure, multiply the feet of elevation by the specific gravity of the outlet liquid.