# A Guide to Selecting the Correct Liquid Pump

## Parameters Required

The answers to the following questions will provide the parameters for the selection of any liquid pump or ProPak system.

#### 1. What is the maximum pressure to be attained?

You need to know the pressure that the system will have to reach, either now or sometime in the future. This does not need to be the usual working pressure, but the maximum pressure ever needed.

#### 2. What is the required flow rate?

You need to know the required flow rate at the required discharge pressure. This is not the flow rate at the maximum pressure, but the flow rate at the working pressure. Remember that every pump has a maximum pressure where it will stall and produce no flow, but at any pressure less than that it will produce flow. This flow reduces in quantity as the output pressure approaches the stall pressure.

#### 3. Is the flow rate constant?

Do you have a process application where you need a constant flow at a constant pressure? If so, then this is expressed as “x” cu.in/m (LPM) @ “y” PSIG (Barg).

#### 4. Is the flow rate decreasing?

Do you have an application where you are testing cylinders or some other vessel to a high pressure. To select the proper pump or ProPak system, you need to know the size of the vessel to be filled. This can be supplied in any form that can be converted to ACF (L).

#### 5. What is the required fill time for the vessel?

It is very common to have an initial fill times that is unrealistic. Many people who are not familiar with high pressure ask for fill times that will require uneconomic systems. Therefore it is important to think about the longest possible fill time the application can stand. Can the cylinder or vessel be prefilled to atmospheric pressure?

#### 6. What is the drive pressure?

This is not the initial pressure in the system first thing in the morning before all of the uses of air are operational, but rather should be the minimum that the plant experiences throughout the day. The pump may have to provide maximum performance when the drive conditions are at their worst.

#### 7. What is the liquid?

Some fluids cannot be pumped with standard pumps. They may require special seals, materials of construction, venting and other considerations. This is also important when very high pressures are required in testing applications to determine the compressibility of the fluid (if any).

## Steps

#### Step 1.

Determine the area ratio required – Outlet pressure divided by air drive pressure

#### Step 2.

Determine a pump series based on the flow requirements.

#### Step 3.

Establish model number whose last stage exceeds the area ratio requirements ascertained in step 1.

#### Step 4.

Use performance curves to select the best model for the application