Graco 3A0868G General Operating Cycle, Dynamic Dosing, Select a Component B Restrictor Size

Setup Mode Details

Dynamic Dosing

In typical operation (ratios 1:1 and above), component A dispenses constantly. Component B dispenses intermit- tently in the necessary volume to attain the mix ratio.

General Operating Cycle, Dynamic Dosing

Overview

Dynamic Dosing provides on-demand proportioning, eliminating the need for an integrator and therefore min- imizing undesired material contact. This feature is espe- cially useful with shear-sensitive and waterborne materials.

A restrictor injects component B into a continuous stream of component A. The software controls the dura- tion and frequency of each injection. See FIG. 52 for a schematic diagram of the process.

Dynamic Dosing System Parameters

The following parameters affect dynamic dosing perfor- mance:

•Component A Flow: Ensure that the supply pump is sized to provide sufficient and uninterrupted flow. Note that component A provides majority of system flow at higher mix ratios.

•Component B Flow: Ensure that the supply pump is sized to provide sufficient and uninterrupted flow.

•Component A Pressure: Ensure precise pressure regulation. It is recommended that the component A pressure be 5-15% lower than the component B pressure.

•Component B Pressure: Ensure precise pressure regulation. It is recommended that the component B pressure be 5-15% higher than the component A pressure.

NOTE: When using dynamic dosing it is very important to maintain a constant, well-regulated fluid supply. To obtain proper pressure control and minimize pump pul- sation, install a fluid regulator on the A and B supply lines upstream of the meters.

Select a Component B Restrictor Size

If you cannot maintain the desired flow and spraying ratio, you may need to select a different restrictor. Use the charts on pages 61 to 65 to select an appropriate restrictor size based on the desired flow and mix ratio.

Balancing A/B Pressure

If component B pressure is too high, it will push the com- ponent A stream aside during B injection. The valve will not open long enough, causing a Ratio High error.

If component B pressure is too low, it will not be injected in sufficient volume. The valve will stay open too long, causing a Ratio Low error.

Selecting the correct component B restrictor size and balancing the A/B pressures will keep the system in the proper pressure range, resulting in a consistent mix ratio.

FIG. 50 shows the A to B pressure balance, read at the proportioner inlet. It is recommended that the compo- nent B pressure be 5-15% higher than the component A pressure to keep the system in the control range, hold the proper mix ratio, and obtain properly mixed material. If pressures are not balanced (“B Pressure Too High” or “B Pressure Too Low”), it may not be possible to hold the desired mix ratio. The system will generate an off ratio alarm and stop operation.

NOTE: In multi-flow rate systems, it is recommended that you set up the system to run properly at the highest flow rate, to ensure adequate fluid supply across the flow rate range.

In dynamic dosing, component A dose valve is con- stantly on. Component B dose valve will cycle on and off; one cycle every 0.5 – 1.0 seconds indicates proper balance.

Monitor system performance by watching the pressure readings for each pump on Run Pump Control (Screen 15).

FIG. 49. Monitor Pump Pressures

Warning messages also provide information on system performance. Adjust pressures accordingly. See Table 2 on page 49.

48 3A0868G