Grain Pan/ Upper Sieve Distribution; Returns Sample; Losses - New Holland CX720 Operator's Manual

Excessive returns will contribute to grain damage due
the additional pass(es) the grain must take through
the drum/concave area. Plugged concave can cause
grain damage because the free grain cannot get out
of the concave area.
Loose elevator chains can also cause grain damage.
It is important to maintain the proper tension on these
chains.
Unthreshed material in the grain tank can be caused
by underthreshing or the lower sieve that is opened
too wide. Increase the drum speed and reduce the
concave clearance as needed to correct the problem.
Reduce also the lower sieve opening slightly to obtain
a cleaner grain tank sample.

Grain pan/ upper sieve distribution

The distribution of material on the grain pan affects
the distribution of material on the sieve. The
distribution on the grain pan should be level to slightly
higher directly under the drum and taper slightly
towards both sides.
The front third of the upper sieve should be
completely clean. The middle third should have some
grain but mostly residue. The rear third of the upper
sieve should have only residue.
If there is some grain on the rear third of the upper
sieve, returns will be increased and there is a
possibility that grain will ride out the back of the
combine. Open the upper sieve to allow more of the
grain to fall onto the lower sieve.
If the material on the upper sieve is broken into small
pieces, the crop is being overthreshed. This can plug
the upper sieve and cause high losses. Increase the
concave clearance and/ or reduce drum speed to
decrease the threshing action.
Unthreshed heads indicate the drum speed should be
increased and/ or the concave clearance should be
reduced. Unthreshed heads can also be caused by
worn rasp bars and worn concaves.
SECTION 3 – FIELD AND SITE OPERATION

Returns sample

It is normal for the return sample to contain a few
unthreshed heads. The purpose of the returns
system is to return unthreshed heads to the threshing
area for another pass. However, a large quantity of
unthreshed heads indicates the concave clearance is
too great.
If the return sample contains a large quantity of clean
grain, the cleaning fan speed should be reduced and/
or the lower sieve should be opened more.

Losses

Losses may occur at different stages: (see fig. 9)
1. Pre-combining losses: (i.e. losses found in
front of the combine) are usually caused by
adverse weather conditions, poor crop conditions
and crop maturity.
2. Header losses: (i.e. losses found behind the
header and outside of the tyres) may be caused
by improper header adjustments.
3. Leakage losses: may be caused by damaged
seals or holes in bottom auger covers.
4. Shoe losses: may be caused by a poor sieve
adjustment, a low cleaning fan speed, or when
working on slopes (exceeding the capacity of the
self levelling system (if fitted).
5. Fan losses: are caused by an excessive
cleaning fan speed.
6. Straw walker losses: These can be unthreshed
ears (underthreshing) or grains, due to poor
adjustment of drum and concave or excessive
ground speed.
Total losses (Lt) caused by the machine:
Lt = (2 + 3) + (4 + 5)+6 – 1
Functional losses (Lf)
Lf = 4 + 5 + 6
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