Bush Hog CBH60, CBH80 manual Hydra ulic Ho Ok-Up C BH 80 Fo, Tractors With Closed- Center Hydraulic

Hydra ulic Ho	ok-Up (C		BH 80) Fo	r	exceed 2800 PSI.
Tractors With Closed- Center Hydraulic					3. A closed-center plug in the b ackhoe control valve
Systems (Figure 21)			drauli c sy stems,		to make it a n on-circulating or a demand				type s ys-
There are two basic types of hy					tem.
open -center and	closed-cente r. The ope n-center				4. A low pressure surge valve in the return line to
system constantly pumps oil thr			ough the hydraulic		keep the tractor back pressure surges from dam-
cylinder operating val ves and returns the oil to the					aging the ba ckhoe control valve seals or tractor
reservoir. The closed-cent er system does not pump					system. A surplus flow line from t he relief valve car-
oil until there is a dem		and f or o il from one of the			ries o nly the excess sur ge oil direct ly back to t he
hydraulic cylinders.					tractor hydraulic r eservoi r so that it			bypasses all
In this case, CL OSED-CENTER m eans that when					other functions.
cylinders are in the neutral position, there is no flow					Backhoe Operation
the operating v alves which control the hydraulic
of oil through the valves. As long a s the engine and					Fot the most p art, a ba ckhoe will function about the
pump are ru nning, a co nstant stan d-by oi l of p res-
sure approx imately 2000 PSI or mo re is maintained					same whether it is powered by an		ope n-center o r
in the system. Press ure oil is av ailable instantly to					closed-center hydra ulic sys tem. Howev er there are
go to work when any one of the ope rating valves is					some diffe rences which t he operator s				hould be
opened.					aware of when utiliz	ing a closed-Ce		nter h ydraulic
Because there must be no flow through the backhoe					system.
					As a backhoe function (lifting, actuating the bucket to
control valve when the levers are in neutral position,
the backhoe must be		converted fo r closed-center			fill it, e tc.) becomes increasingly di			fficult a nd the
operation.					hydraulic system pressure is rising closer to its maxi-
					mum setting, ther e wil l be a noticeab			le slow do wn
Hook-Up Requirements					before stopp age occurs. As the system pressure is
					approaching maximum, the pump is also				beginning
The hook-up of the CBH 80 Backhoe to the closed-					to str oke back for less and less fluid			delivery. At
					maxi mum p re ssure, th e pu mp is completely
center system requires more th an conn ecting it to					destroyed and there is no delivery.
the remote couplers. The required devices are:					Therefore, when working various backhoe functions
1. A flow r estrictor in the pressur e li ne to keep				the
					at or near maximum ability, a closed center system
speed of the backh oe operatio n within s afe and					will g ive t he o perator th e impression that the bac k-
acceptable limits.					hoe is sluggish a	nd somewha	t unresponsive.
2. The main relief valve in the backhoe control valve					Learning to e ase up slight at t he first i ndication of
					slow down will permit the backhoe to perform at con-
must be replaced with plug, to allo w tractor system					tinuing maximum speed and efficiency.
relief to control pressure. System pressure must not
Figure 21			To Tractor		Surge Relief
			Reservoir		Valve
	Replace Main Relief with
		Closed-Center Plug.
						Couplers
					Hoses Supplied
Replace Open-Center Plug					by Customer
with Closed-Center Plug,
Shown.

41