Got our brush hog, got a question

[RandyS]

Welded our mini skidsteer plate onto your plate. Seems to turn the blades fine.
The question my partner has is, does it do harm to the motor on the brush hog when you turn off the hydraulic flow to the brush hog and it stops it abrubtly?
Thanks.

 

[SnowRidge]

Most of us throttle back (when we remember to do and it's feasible) before turning the PTO on or off with the 48" brush hog attached. It's because of the way the blades slam into the stops.

 

[ponytug]

That falls in the not recommended category. Your PTO pressure relief may be more effective than the PT's, but your hydraulic motor will last longer if you don't do it.

If your PTO switches to neutral (i.e. spools), it wouldn't matter, but from the "...stops it abruptly..." comment, I don't think it does.

I try always to switch on and off the PTO at idle.

All the best,

Peter

Welded our mini skidsteer plate onto your plate. Seems to turn the blades fine.
The question my partner has is, does it do harm to the motor on the brush hog when you turn off the hydraulic flow to the brush hog and it stops it abrubtly?
Thanks.

 

[J_J]

Welded our mini skidsteer plate onto your plate. Seems to turn the blades fine.
The question my partner has is, does it do harm to the motor on the brush hog when you turn off the hydraulic flow to the brush hog and it stops it abrubtly?
Thanks.

You should be using a motor spool valve, which will let the motor wind down. If it stops suddenly, sooner or later something is going to break, it could be a valve or motor, or hydraulic line. I would add a manual motor valve which would let you control the speed or an electric valve in order to let the attachment coast to a stop. An electric valve will apply hydraulic fluid rather quickly. It is either full on or off.

 

[cqaigy2]

On the 422 the brushmower spools down when the switch is flipped off. I do turn it on at low idle though.

 

[J_J]

On the 422 the brushmower spools down when the switch is flipped off. I do turn it on at low idle though.

It winds down because it is an open center valve. Fluid from the motor recirculates through the open center portion of the valve.

Open-Center: Typically used with a fixed-displacement pump, allows oil to free-flow back to the tank in neutral position. Shifting the spool redirects oil to the selected work port.

Northman Fluid Power Hydraulic Directional Control Valve – 16.8 GPM, 4500 PSI, 3-Position, Double Solenoid, Open Center Spool, 12 Volt DC Solenoids, Model# SWH-G02-C3-D12-10 | Power Solenoid | Northern Tool + Equipment

 

[KMA]

It winds down because it is an open center valve. Fluid from the motor recirculates through the open center portion of the valve.

So is it okay to do then with this type of valve, or still recommended against? I throttle down first anyway out of habit, but it would be a good thing to know.

 

[Rivco]

You should be using a motor spool valve, which will let the motor wind down. If it stops suddenly, sooner or later something is going to break, it could be a valve or motor, or hydraulic line. I would add a manual motor valve which would let you control the speed or an electric valve in order to let the attachment coast to a stop. An electric valve will apply hydraulic fluid rather quickly. It is either full on or off.

The PT 180's have the manual PTO valve and IMHO is a much better setup...it eliminates the slam bang effect. I did not have to throttle down because I could engage the PTO very slowly or fast as needed. I like having that control...plus if the electric PTO toggle switch ( on 422's, 425's, and big red's) craps out while you are running the brush mower, stump grinder, power auger, etc. your only choice for disengagement is to shut down the machine.

 

[ponytug]

Yes, if you have an open center, then there is no surge in hydraulic pressure as you shut off power to the motor, and you can shut it off with the engine powered up. With a spooled center, the two ports on the motor are connected together so as one develops pressure, the other pumps it away, and there is no hard stop.

The converse is not true. If the mower is stopped, and the engine is at speed, and you flip the switch on, you will slam the motor with full hydraulic flow.

Basically, you are trying to prevent what is known as 'water hammer' in plumbing, abruptly opening or shutting a valve that would cause a hydraulic surge against a fixed object. (i.e. a pressure surge against a valve, or your motor.)

Does this help?

I'd stay with the old habit; it will help you in other situations, such as a PTO hose not being completely on or...

Have fun!

Peter

So is it okay to do then with this type of valve, or still recommended against? I throttle down first anyway out of habit, but it would be a good thing to know.

 

[J_J]

So is it okay to do then with this type of valve, or still recommended against? I throttle down first anyway out of habit, but it would be a good thing to know.

It appears that you have a closed center valve because of the instant shut off. If you want to keep it as is, then throttle down and shut off the fluid to the front attachment. Any attachment that has a lot of residual centrifugal force will still try and spin, and if the fluid is shut off instantly, something bad may happen. I thought those skid steer machine had a motor spool valve up front just for that reason.

On the sudden rush of hydraulic fluid, it is not that hard of a start, because the hydraulic fluid only builds up pressure when it see any resistance to the flow, which would be the hydraulic motor. It then ramps up at a fast rate. The PT units that have the switch to turn on the attachment, have been doing this for a while and don't seem to be having any problems.

I also have the manual hydraulic speed control on my 1445. I can set it to any speed up to the maximum .