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Hydraulic Draft Control: The Plough That Rises When the Soil Gets Hard

Henry George Ferguson, Belfast · Public domain (expired patent)

أنشأه

Martin

27. سبتمبر 2026

Hydraulic Draft Control: The Plough That Rises When the Soil Gets Hard

Harry Ferguson's linkage made a mounted plough follow the steering and press the tractor's rear wheels down. The next step was to make the tractor hold the plough in the ground by itself. US 2,118,180, *Tractor for Agricultural Implements*, filed 27 January 1937 (British priority 5 February 1936) and granted 24 May 1938, lets the draft of the implement work the hydraulic valve. The top link pushes on a heavy spring. When the plough bites into harder ground the draft rises, the spring compresses, and the valve lets oil into the pump, which lifts the implement a little until the draft falls back and the valve returns to its "dead point". When the draft falls, the release port opens and the plough sinks back. The valve works on the pump's suction side so the oil is not churned under pressure all day. This rung simulates draft control against position control, measures a tine's draft against depth in a sand tray, and builds a spring top link that shows the signal.

متوسط

About 4 hours

التعليمات

Draft control against position control

جارٍ تحميل دفتر Jupyter…

The linkage it controls

Draft control works through the Ferguson linkage. The embedded blueprint shows how the links' geometry makes the implement follow the steering and load the rear wheels.

Read the control from the patent

Sheet 1 of US 2,118,180 shows the rear of the tractor in section: the upper link and the lower links carrying the implement frame, the ram that lifts them through a crank and lift arms, and a pump with **four pistons**. The upper link acts on a heavy compression spring 29. Through rods and a spring-loaded lever the spring's movement reaches a **piston valve** in the pipe to the pump's suction. The valve is so long, and its ports so spaced, that at its mid-position — the "dead point" — it covers both the suction ports and the release ports, so "movement of the fluid can be prevented in either direction". The patent adds a damper on the valve, because some implements moved it "more than necessary", and a safety spring so the hand lever cannot force the mechanism. A stop on the ram cuts the supply at full height.

Measure draft against depth

Fill a tray 120 mm deep with damp sand and pack it evenly. Bend a tine from a 20 mm spring steel strip: an upright shank with a short forward-pointing foot. Clamp the shank in a block you can set to a depth of 20, 40, 60 and 80 mm. At each depth pull the block 400 mm through the sand at a steady walking pace with a spring scale, and read the steady pull. Repack the sand between runs. Plot pull against depth: it rises steeply. Fit a line and use its slope in the notebook in place of the soil numbers — that is your sand's own draft law.

المواد لهذه الخطوة:

رمل ناعم20 kilogram

ماء2 لترات

شريط فولاذ نابضي1 قطعة

لوح خشب رقائقي1 قطعة

الأدوات المطلوبة:

مقياس قوة (ميزان زنبركي)

مسطرة

ملزمة منضدة

قدمة رقمية 6 بوصات

Build a spring top link that shows the draft

Make a top link from two telescoping pieces of PVC pipe with a compression spring between them and a pointer on the inner piece reading against a scale on the outer. Calibrate it by loading it end-on with the spring scale. Mount it as the top link of a small three-point frame on a plywood 'tractor', with the tine from step 4 as the implement below, so that the tine's draft tips the frame and pushes on the top link. Pull the rig through the sand tray: the pointer moves as the draft changes. Mark a dead band either side of your chosen setting and, by hand, raise the tine a notch whenever the pointer leaves it on the high side and lower it when it leaves on the low side. You are the valve — and you will find the tine rising in packed patches, as the notebook predicts.

المواد لهذه الخطوة:

أنبوب PVC1 متر

مجموعة نوابض ضغط1 قطعة

لوح خشب رقائقي1 قطعة

براغي آلية10 قطع

الأدوات المطلوبة:

مقياس قوة (ميزان زنبركي)

مسطرة

مثقاب لاسلكي

طقم لقم ثقب

قلم تعليم ثابت

One correction, as the patent describes it

مساحة عمل Blockly

Loading Blockly workspace...

A draft-controlled hitch that misbehaves

Hitch hydraulics faults, from the most common.

Flow

History and context

**Henry George (Harry) Ferguson** of Belfast filed **US 2,118,180** on 27 January 1937, with British priority of 5 February 1936; it was granted 24 May 1938 and refers to his earlier power-unit patent 1,687,719. The Ferguson-Brown tractor of 1936 and the Ford 9N of 1939 carried the Ferguson System — three-point linkage with hydraulic draft control — and draft control became standard on farm tractors. **Honest limits.** Draft control holds the pull, not the depth: in variable soil the plough runs shallower where the ground is hard, which is sometimes not what the farmer wants; later tractors mix draft and position control. The notebook's soil is a simple model. Never work under a raised implement held only by hydraulics.