b77 backhoe question

[BotaDriver]

Twice I've read the pressure washer analogy and twice I found it of ZERO use in what GPM does for a given tractor.

If the issue with GPM was as simple as that, we'd all have 30+ GPM pumps on our small tractors.

Increasing the GPM of any tractor is the same thing as increasing the breaker size on a circuit. If you have no use for a larger breaker, and you install it, are you achieving more work? NOPE

Tractors are stated to do certain things...lift x pounds to a certain height at a certain time. That's what it's designed to do. Looking at the GPM of a tractor is good for one thing, IMPLEMENTS. If you need a certain flow for a certain implement, find a tractor that has that flow on it's AUX circuit. Do not look at combined; it's a worthless number. Any sales guy that tries to use a combined rating as a selling tactic is a moron, and you should run away from them fast. Implements that typically need large flow are ones that have motors on them that typically spin something at a good rate. A Hydro broom, or hydro bush hog are examples of where high GPM is needed to achieve proper use. Some smaller brooms don't matter. That's where the PTO is handy though; it's inefficient to use the motor to turn a pump that then turns a motor (hence the HST models drinking more fuel than gear units).

So RESEARCH attachments you want / need and see what they require. Items like grapples need 7GPM tops to work quickly.

 

[SteveF]

Twice I've read the pressure washer analogy and twice I found it of ZERO use in what GPM does for a given tractor.

If the issue with GPM was as simple as that, we'd all have 30+ GPM pumps on our small tractors.

Increasing the GPM of any tractor is the same thing as increasing the breaker size on a circuit. If you have no use for a larger breaker, and you install it, are you achieving more work? NOPE

Tractors are stated to do certain things...lift x pounds to a certain height at a certain time. That's what it's designed to do. Looking at the GPM of a tractor is good for one thing, IMPLEMENTS. If you need a certain flow for a certain implement, find a tractor that has that flow on it's AUX circuit. Do not look at combined; it's a worthless number. Any sales guy that tries to use a combined rating as a selling tactic is a moron, and you should run away from them fast. Implements that typically need large flow are ones that have motors on them that typically spin something at a good rate. A Hydro broom, or hydro bush hog are examples of where high GPM is needed to achieve proper use. Some smaller brooms don't matter. That's where the PTO is handy though; it's inefficient to use the motor to turn a pump that then turns a motor (hence the HST models drinking more fuel than gear units).

So RESEARCH attachments you want / need and see what they require. Items like grapples need 7GPM tops to work quickly.

I'm not really clear what you are asking... how about an example using an air tool. Among other spec's, air compressors are rated at delivering "x" CFM at a certain PSI. Most compressors can easily generate 100 to 150 PSI but you have to invest the big bucks to get bigger CFM output. Air tools are rated to operate at a certain PSI range while consuming a certain cubic feet per minute of air. If you have ever tried to operate a pneumatic lug wrench at less than the needed CFM, you may not be able to generate sufficient force (ft lbs) to break the nut loose. If you manifold two pneumatic lug wrenches to the same air hose, the pressure remains fairly constant but the amount of work (eg ability to crack a nut loose) is roughly cut in half.

I may have confused the issue but I'm going to hit "submit reply"

 

[BotaDriver]

I'm not really clear what you are asking... how about an example using an air tool. Among other spec's, air compressors are rated at delivering "x" CFM at a certain PSI. Most compressors can easily generate 100 to 150 PSI but you have to invest the big bucks to get bigger CFM output. Air tools are rated to operate at a certain PSI range while consuming a certain cubic feet per minute of air. If you have ever tried to operate a pneumatic lug wrench at less than the needed CFM, you may not be able to generate sufficient force (ft lbs) to break the nut loose. If you manifold two pneumatic lug wrenches to the same air hose, the pressure remains fairly constant but the amount of work (eg ability to crack a nut loose) is roughly cut in half.

I may have confused the issue but I'm going to hit "submit reply"

It's sort of like air tools, except it's using rams / cylinders to do most work. Outside of HST, you will not find many, if any of the users on the board who have hydraulic driven motors. Utility tractors, and variants thereof typically have a PTO. PTO operated attachments win over hydro attachments for these machines hands down. It's inefficient to use hydro motors, and these little tractors need all the HP they can get for some of the 3pt attachments we run. Using PTO would be like taking the motor off your compressor and hooking it directly up to the tool you want to run. If you do go that route, you will have considerably more power at the tool due to how inefficient it is to use compressed air as a power source (5 to 10x more power). The heat coming off the compressor is wasted energy.

Using Hydro power over the PTO will drop the power down by at least 20%. If you have 30HP @ the PTO, decide to drive a hydro pump and then a motor on an attachment, you will not get any more than 24HP out of the attachment.

When looking at the loss of a HST transmission, a gear 3240 should put down as much or more power than the 3940 HST. A big difference when you look at it like that.