facility flexible hose and the trailer air inlet line to the blower. With
the blow down valve still open, close the aeration and/or top air
valve, open the pressure control/proportioning valve (directing all the
air to the silo) and engage the blower. The line gauge should have a
reading of 2 psi or less. A reading of more than this could indicate
poor piping, a blockage in the line or inadequate venting of the
storage facility. All of these factors would affect unloading time.
29

NOTICE
Do not close a valve unless the air is directed in another path. Dead
heading the blower can cause serious damage and injury.

Next, begin to pressurize the vessel to unload. Close the blow down
valve, open the top air valve and/or aeration control valve and close
the pressure control/proportioning valve, you are now routing all the
air into the vessel. Monitor the tank gauge to ensure that the
maximum allowable working pressure (MAWP) is not exceeded. The
MAWP is stamped on the VIN plate. If you have a question regarding
the MAWP of your tank, by all means, call the factory at 1-800-4006913. Once operating pressure has been reached, open the
proportioning valve halfway and the slowly open the center product
valve since the center hopper holds the most product. The best
unloading times will be accomplished when the pressure drop during
this initial process is kept to a minimum. Continue to monitor the
gauges and adjust the proportioning valve as necessary to maintain
approximately 14-15 psi in the tank. Opening the proportioning valve
decreases tank pressure and increases discharge line airflow, while
closing of the proportioning valve will increase tank pressure and
decrease airflow in the product line. Too little airflow in the discharge
line will promote line plugging.
As unloading commences, the tank gauge should begin to rise and
settle back to the initial pressure and the line gauge should now show
approximately one pound less than the reading on the tank gauge.
The tank gauge should be steady, while the line gauge will show
some fluctuation as the product moves through the line. A steady,
slow rising line gauge is usually an indication of a plugged line. How
to deal with a plugged line is addressed on page 38.
Continue unloading the trailer until the line and tank gauges show a
pressure drop of approximately four pounds. At this point, slowly
open one of the remaining hopper valves and the quickly close the
previous one. During this operation, the best unloading times will be
afforded the operator who has the least pressure drop during this
step.

30

Repeat the operation for the remaining hoppers until all hoppers have
been unloaded.
When the last hopper has been unloaded, product will have settled
back into the other hoppers during the unloading process. Repeat
the unloading sequence, starting again with the middle hopper and
proceed as before, monitoring gauge pressures. Continue the
operation at each hopper until it is impossible to maintain tank
pressure. This will unload any remaining product from the trailer.
At this point, the trailer is unloaded.
Open the blow down valve (depressurizing the tank) and bring tractor
R.P.M. back to idle. Allow the blower to cool as the tractor idles.
When the blower has cooled down disengage the P.T.O. and remove
the air inlet hose from the blower. After all pressure has been
relieved from the tank and line as indicated by the gauges,
disconnect the discharge line from the storage facility line. Reattach
dust cap and place hoses in hose tubes if appropriate. Close all
valves, except blow down valve.

Step by steps instructions are located on the following pages.

31

UNLOADING—STEP BY STEP
NOTICE
Never discharge payload into a storage facility of unknown contents
or capacity. Check to ensure that the storage facility will accept the
total payload.
1.

Position trailer for optimum unloading. See page 29.

2.

Retrieve discharge hose and connect it to the discharge line. Attach
opposite end of hose to adapter on storage facility fill line.

3. Open the pressure control valve.
4. Engage blower or compressor.

DANGER
When unloading, the discharge hose must be secured at both ends
prior to pressurizing unit. A loose hose will bull whip potentially
causing injury.

NOTICE
When pressurizing unit, look for air leaks. If any are found, shut
down immediately relieve pressure from the tank and line.

5. Open all aeration valves and close pressure control valve and blow-down
valve. Pressurize unit. If cargo does not require aeration, open the Top
Air supply valve to pressurize the unit.
6. When unit has reached operating pressure open the proportioning valve ½
to ¾ of full open.
7. SLOWLY open discharge valve on center hopper.
8. Adjust the pressure control valve to maintain maximum operating
pressure and slight movement of discharge hose.
9. Close the front and rear individual hopper aeration control valves, on units
so equipped.
14. Readjust pressure control valve if necessary.

32

10. When tank pressure begins to drop rapidly, open the aeration valve on
the front hopper.
11. SLOWLY open the discharge valve on front hopper.
12. Quickly close the center hopper discharge valve.
13. Close the aeration valve on center hopper.
14. Readjust pressure control valve.
15. When tank pressure begins to drop rapidly, open the aeration valve on
the rear hopper.
16. SLOWLY open rear hopper discharge valve.
17. Quickly close the front hopper discharge valve.

DANGER
Do not exceed working pressure. If pressure rises above limits, shut
down immediately and investigate.
18. Close aeration valve on front hopper.
19. When tank pressure begins to drop rapidly, close rear discharge valve.
20. Purge unit by opening all aeration valves and opening and closing
discharge valves rear to front.

CAUTION
Before opening blow-down line, make sure no one is in line of air
stream.

21. Open blow-down line to return the unit to atmospheric pressure.
22. Disengage blower or compressor.

DANGER
Always relieve pressure in discharge hose before disconnecting it.
23. Disconnect and stow discharge hose.
24. Close all valves except the blow-down valve.

33

NOTICE
Variations or deviations to the unloading procedure may be
necessary due to the type of product being unloaded or the nature of
the unloading site. Operating more than one hopper at a time is
common with extremely large capacity blowers or a combination of
compressor and blower only. A second and third hopper can be
activated to maintain desirable product to air mixture.

OPERATING TIPS

MINIMIZING UNLOADING TIME
Unloading time will depend, however, on variables such as type of
product being unloaded, unloading site, condition of equipment, etc.
The following points should be considered.
1. Vertical positioning of discharge hose results in smoother product
flow. Product tends to “settle” in portions of hose which runs
horizontally (see Figure 6). This accumulation of product will
restrict product flow, will increase unloading time, and may
eventually clog the line. Ideally, the product will would change to
vertical immediately after leaving the trailer into the storage line
with zero elbows. Since having no elbows in the line may not be
practical, all bends or elbows should be sweep types having a large
radii. The radius should be 15x the pipe diameter.

Figure 6. Product Flow and Build Up

34

Comparing product flow through a hose in the vertical portion of hose
(Figure 7). It can readily be seen that vertical positioning of hose
results in smoother product flow.

Figure 7. Vertical
Product Flow

NOTICE
If discharge hose must be run horizontally for any considerable
distance, elevate the hose at intervals to create slight “humps” in the
hose. This will help keep the product flowing freely.

35

2. The relative density (product to air ratio) decreases as the

elevation increases. The higher the storage facility, the longer it
will take to unload. Figure 8, illustrates the relative density at
various elevations. Note that as the product head decreases, the
air velocity will increase and air pressure will decrease.

Figure 8. Relative Density at Various Elevations

3. Heavy, fine materials such as sand or sugar require considerably
more unloading time. Light, bulky products offer more resistance
and are more easily carried by the air stream. Use the pressure
control valve and the product discharge valve to maintain the
optimum product-to air ratio for the type of product being
unloaded.
4. Avoid abrupt, unnecessary changes in pipe diameter, especially
increases in diameter of pipe spanning long conveying distances.
Increasing pipe diameter allows the air in the line to expand, thus
causing a loss of pressure. Although conveying distance is a
function of both air volume and pressure, effective conveying
distances will be decreased with sudden pressure drops.

36

Example of Good Piping Techniques

GOOD PIPING
A.

Keep as short as possible

B.

Strictly vertical and horizontal alignments.

C.

Minimize bends.

D.

Give bends 4’ or 5’ radius (or 15x diameter of pipe).

E.

Adequate venting of receiving bin (min. 12” diameter).

F.

Ample ground clearance (4’-6’) at hose hook up.

G.

Tight and smooth joints.

H.

Use 5” long when high unloading rate is required (assume adequate CFM).

BAD PIPING

EFFICIENCY REDUCTION

I.

Sharp turns or elbows.

15-25%

J.

Useless bends or turns

10-20%

K.

Shut-off or diverter valves in line.

8-10%

L.

Longer line than necessary.

8% per 10’

M.

Diagonal piping.

10-20%

N.

Inadequate venting.

30-50%

O.

Fill pipe at bottom of hopper.

P.

Reduction in pipe size.

Q.

Horizontal hookup connection.

Exponential
30-50%

37

HOW TO UNPLUG A LINE
Cleaning of a plugged line without uncoupling the product hose is
easy with a Heil trailer. Proper manipulation of the valves directs all
the air from the blower into the plugged line. Air in the pressurized
line is then released through the product valve into the
non-pressurized vessel, pulling a portion of the plug into the tank.

The line is plugged when the line pressure becomes steady and the
tank and line pressure rise together. All movement of the product
hose is stopped.
Step 1: Completely close the product discharge valve.
Step 2: Close Aeration Control Valve.
Step 3: Fully Open the Pressure Control Valve.
If the line pressure does not drop off within a few minutes (indicating
product flow), open and close the pressure control valve quickly
several times, creating surges of air into the product line.

If the line doesn't clear, follow the steps on the next page...

38

The following steps are shown in a graphic on the next page…

Step 1: Close all product valves.
Step 2: Stop blower.
Step 3: Open blow down valve. (Leave it open)
Step 4: Open pressure control valve.
Step 5: Close aeration control valve.
Step 6: Close top air valve (if equipped with one).
Step 7: Re-start the blower.
Step 8: Allow line pressure to build up to 15 PSI.
Step 9: Quickly open the product valve of the most empty hopper.
Part of the product plug will rush back into the open hopper.
Step 10: When line pressure is zero, close the product valve and
allow the line pressure to build back up to 15 PSI.
Step 11: Quickly open the product valve again.
Step 12: Continue this procedure, eroding away at the plug each
time, until the line is clear and the pressure in the line does not build
up.
Step 13: Once clear (line pressure will not build up), close the hopper
valve, open aeration valve, close blow down valve—the tank is now
pressurizing, resume unloading procedures.

39

40

Recommended Airflow Volumes for
Various Bulk Density Products
Nature of Product:
Density, Particle Size, etc.

Approximate Airflow
Requirement: 1Cubic Feet per
minute (CFM)

Light density pulverants up to 40
lb/ft3 (flour, lime, etc. having
good aeration characteristics).

Best handled with 190-200 CFM
air. Can be conveyed efficiently
at tank pressure of 12-25 psi.

Medium density pulverants 40 lb/
ft3 - 60 lb/ft3 (talcum powder
which has good aeration
characteristics).

Best handled with 225-325CFM
air. Can be conveyed efficiently
at tank pressure of 12-25 psi.

Best handled with 275-400 CFM
High density pulverants 80 lb/ft3
- 110 lb/ft3 (talcum powder which air. Can be conveyed efficiently
has good aeration characteristics). at tank pressure of 12-25 psi.
Small granular 40 lb/ft3 - 80 lb/ft3 Best handled with 450-550 CFM
(table salt, beet sugar).
air. Can be conveyed efficiently
at tank pressure of 10-15 psi.
Medium granular 40 lb/ft3 - 80 lb/
ft3 (wheat, corn, pebble lime).

Best handled with 475-600 CFM
air. Can be conveyed efficiently
at tank pressure of 8-12 psi.

Course granular (.25” - 1.5”
particle size.)

Air volume and pressures for
conveying these products
depend on particle size, bulk
density and distance to be
conveyed. Typically requires
greater than 500 CFM and

Table 1. Pressure and airflow requirements for various bulk
density products.
1

Figures based on 15 psi blower outlet pressure and 4 inch discharge
line.

41

Calculation of Blower Speed Based on Product
Requirements
Once the airflow requirement for a particular product has been
established, a cross reference on the blower make must be performed
to secure the required blower speed for the production of the
necessary volume of air. Knowing this, the required engine speed
can be calculated for the situation, if the make and model of both the
transmission and the selected power take off (PTO) are known. The
details of the PTO (location on the transmission, etc.) are defined
once the transmission type is determined.
Example:
Given: Product to be hauled is Portland Cement. It will be unloading
using a Gardner-Denver T5CDL9 blower.
Required: Calculate the engine speed needed to produce the
required air volume from the blower to effectively convey the cement.
Assume: Operating pressure will be 15 psi and 4 inch discharge line
will be used.
Solution: From the Product Bulk Densities beginning on page 44,
we find that Portland Cement has a bulk density of 94 lbs/ft3. Now,
cross referencing this bulk density to the Recommended Airflow
Volume for Various Bulk Density Products on page 41 we find
that the required air volume for the products having this bulk density
averages 338 CFM.
From the blower manufacture’s product literature, we find that the
closest mat at 15 psi is 375 CFM at 1500 RPM blower speed. This is
what we will design around.
Now, we need to know the make and model number of the
transmission to cross reference a power take off in order to determine
the ratio of the PTO.

42

The make and model number of the transmission and make, model
number and location of the PTO are cross referenced in the PTO
Manufacture’s Guidebook in order to secure the final ratio. The
tractor manufacture should also be able to help with this information.
PTO final drive ratios typically average 130% to 180% for dry bulk
service. What this means is that the PTO turns 80% faster than the
engine.
For the sake of this discussion, assume we have a PTO of 180%. We
calculate the necessary engine RPM by the following.

Blower RPM
PTO Ratio

X 100 = Engine

Substituting our values, we have:

1500 RPM
180%

X 100 = 833 Engine

Therefore, to ensure that we are supplying an adequate supply of air
to our trailer system, then engine of the tractor must turn 833 RPM
with this PTO. With the tractor engine turning so few RPM efficiency
may be sacrificed. Therefore, it may be necessary to select a PTO
with a lower ratio to ensure that the engine turns fast enough to
operate within its power band and at the highest efficiency possible.
Selecting a PTO with a 130% ratio brings engine speed up to 1154
RPM, which may be better on the engine from an efficiency and,
hence fuel consumption standpoint.

43

Product

Lbs. /
Cu.
Ft.

Product

Alfalfa Meal

14-22

Basalt

Alfalfa Pellets

41-43

Bauxite, Dry, Ground

Lbs. /
Cu.
Ft.
80-105
68

Alfalfa Seed

10-15

Bauxite, Crush-3

75-85

Almonds, Broken

28-30

Bauxite, Mine Run

66-90

Almonds, Whole Shelled

28-30

Beets, Whole

Alum, Fine

45-50

Bentonite, Crude

Alum, Lumpy

50-60

Benzene Hexachloride

Alumina Fines
Alumina
Alumina Sized or Briquette

35

Blood, Dried

48
35-40
56

35-45

50-65

Blood, Ground

30

65

Bones, Whole

35-50

Alumina Chips, Oily

7-15

Bones, Crushed