jinman
Rest in Peace
- Joined
- Feb 23, 2001
- Messages
- 20,387
- Location
- Texas - Wise County - Sunset
- Tractor
- NHTC45D, NH LB75B, Ford Jubilee
I believe your tractor actually has at least three pumps and maybe even four. As indicated in the specs, you have a power steering pump and a hydraulic implement pump. The implement pump will provide hydraulic power for the 3PH, FEL, and remote hydraulic connections if installed. It may also provide power for a backhoe through a power-beyond circuit.
Most hydrostatic transmissions that I am familiar with are both pump and hydraulic motor in one integral package. Sometimes these transmissions will also have a booster pump feeding the main hydraulic pump. By changing the foot pedal position, you change the amount of fluid the HST's pump supplies to the motor. This is normally done by a swashplate in a variable displacement pump. In some hydrostatic transmissions, the speed of the motor is also variable.
So I think your HST is a separate pump from the ones listed in the spec sheet. It's gpm flow is not specified because it is a variable amount and not the way the HST is rated.
As far as filters, the reservoir for power steering is normally separate from the main hydraulic reservoir. The main hydraulic reservoir holds fluid for the implement pump and hydrostatic transmission (as well as the mechanical gears and differential). There may be a main hydraulic filter and an additional filter for the HST transmission. That is the case on my tractor. The input fluid on my HST transmission is filtered to remove any particles that may not be trapped in the main filter. HSTs often have very critical clearances and need very clean fluid for long life.
I'm not sure why the power steering on a tractor is called "hydrostatic" while the 3PH is called a "hydraulic" lift. It would seem you could also call it a hydrostatic lift. Maybe it has to do with the way the input generates an offset into the servo system that causes it to drive until it nulls out the input signal. On this I'm just not sure and your guess is as good as mine. /forums/images/graemlins/smirk.gif
Most hydrostatic transmissions that I am familiar with are both pump and hydraulic motor in one integral package. Sometimes these transmissions will also have a booster pump feeding the main hydraulic pump. By changing the foot pedal position, you change the amount of fluid the HST's pump supplies to the motor. This is normally done by a swashplate in a variable displacement pump. In some hydrostatic transmissions, the speed of the motor is also variable.
So I think your HST is a separate pump from the ones listed in the spec sheet. It's gpm flow is not specified because it is a variable amount and not the way the HST is rated.
As far as filters, the reservoir for power steering is normally separate from the main hydraulic reservoir. The main hydraulic reservoir holds fluid for the implement pump and hydrostatic transmission (as well as the mechanical gears and differential). There may be a main hydraulic filter and an additional filter for the HST transmission. That is the case on my tractor. The input fluid on my HST transmission is filtered to remove any particles that may not be trapped in the main filter. HSTs often have very critical clearances and need very clean fluid for long life.
I'm not sure why the power steering on a tractor is called "hydrostatic" while the 3PH is called a "hydraulic" lift. It would seem you could also call it a hydrostatic lift. Maybe it has to do with the way the input generates an offset into the servo system that causes it to drive until it nulls out the input signal. On this I'm just not sure and your guess is as good as mine. /forums/images/graemlins/smirk.gif
