Mowing 48" Finish Mower Questions

[Schultz]

Re: 48\" Finish Mower Questions

That makes it easier, and the above formula will work. I did some digging since I have an interest in owning a PT some time next year.

Using the numbers you gave me the motor is a Gresen high-speed geroter motor. .45 in3/revolution
8 gal = 1848 in3 - from PT's 8 gpm pto
1848/.45 = 4106 rpm

Gresen motor

PT's 8 gpm max pto output provides 4106 rpm at the motor shaft, which is also the blade spindle.

With a 17" blade diameter, I guessing at the blade diameter, but please post the actual diameter.

This provides a very respectable blade tip speed of:
17/12*4106*3.14 = 18,264 ft/min

Now this calculation doesn’t account for the volumetric efficiency of the motor. If the motor is only 90% efficient then the blade tip speed drops to 16,438 ft/min.

 

[SnowRidge]

Re: 48\" Finish Mower Questions

<font color="green">( Gresen motor

PT's 8 gpm max pto output provides 4106 rpm at the motor shaft, which is also the blade spindle.
With a 17" blade diameter, I guessing at the blade diameter, but please post the actual diameter. )</font>

I found that page too. The listed motor is not identical to the one PT uses. The mount is different, I think (BB1A3 vs. BA1A3).

Interestingly, the motor says Parker on it, not Gresen. However, I couldn't find that part number in the Parker catalog. Did Parker buy Gresen?

The blade diameter is 16 1/2 inches, measured cutting tip to cutting tip. The blade is not quite rectangular.

SnowRidge

 

[smartguyz]

Re: 48\" Finish Mower Questions

Hi Schultz,

Pretty decent tip speed!

I note from your profile that you have an ingersol tractor with a hydro-vac attachment. Do you think that this can be adapted to make the PT 48" finish mower deck into a convertible bagger system? I just finished sending away for an ingersol catalog and speaking to their salesperson, I am of the opinion that this might be doable. Since you own one, what's your take on this?

I spoke to Kristie a couple of weeks ago, and suggested that a bagger assembly for their decks might be a popular item. She just said she'd take a note on the suggestion. I'd like one just for the yearly bagging of the output of all my trees, which drop just a huge load of leaves around the property every year. Having the PT do duty here would be wonderful.

Anyone have thoughts along these lines?

-Rob /forums/images/graemlins/grin.gif

 

[MossRoad]

Re: 48\" Finish Mower Questions

Hey, Rob... nice picture in your signature! /forums/images/graemlins/smile.gif

I think a leaf pickup system would be awsome for landscapers and folks with lots of trees. My guess is it would be pretty expensive, but worth it to some.

 

[Schultz]

Re: 48\" Finish Mower Questions

<font color="blue"> </font>

Indeed, even with a 16.5" blade the tip speed is in the neighborhood of 17,700 ft/min.

Like you, I have the yearly dump of oak & maple leaves. This was one of the main reasons I bought the vacuum. I don't think I could justify the new price of somewhere in the $1200 range. I was patient and asked a couple of the dealers to call me when one became available. I paid $350 used, it was used very little since the paddle wheel and inside housing still had much of its paint on it. I also use this to pick up grass clippings in the summer that I add as mulch around tomatoes and other plants. After that, it's removed and sits in the corner until fall.
Unfortunately the Ingersol vacuum isn't designed for the 60" deck, I had to modify it to work with mine. When the grass is heavy, I have to go slower or take less of bite. The 6" hoses will plug with grass or debris at the mower deck hose bend. Since my use is limited, I haven't spent much time on it to solve the problem. I think if I used 8" hoses and adapted it down & up at the vacuum housing, the hose probably wouldn't plug. To answer your question: Now that I know its limitations, it never or rarely plugs for me and I really like it for leaf and heavy grass pick up. My wife doesn't care for it because it plugs a lot for her, and I don't think she has used it in couple of years. She does 95% of the mowing.

I plan to keep the lawn vac and use it on a future PT. One of the other guys has made lawn vac to fit his 60" deck, but uses an engine driven vacuum. With the Ingersol unit you may need to change the hydraulic motor to speed it up, the Ingersol unit works on 9.5 gpm, so PT's 8gpm may be too slow? But in concept it would be placed in series to the mower. Some other posts, I saw a link to Walker mowers, they too have a rear discharge collection system and maybe some parts could be scavenged off their machines?
We need to hound the guy that has the vac system on his PT to post some pictures.

 

[SnowRidge]

Re: 48\" Finish Mower Questions

<font color="green">( ( Dose PT use different hydraulic motors for the two different decks? )

Don't know--yet. Our 48" has a MGG20020 BB1A3 motor. Anyone with a 60" care to take a look and post what you find? )</font>

Found this 60" motor reference in another thread: Gresen MGG20025BB

SnowRidge

 

[Schultz]

Re: 48\" Finish Mower Questions

Thanks for the part number.

Just for completness, I'll put the 60" calculation here so it's all in one thread and I'll use a 20.5" blade. If anyone has the exact size, they can chime in.

The MGG20020 BB1A3 motor is a .58in3/rev motor

1848 in3 = 8 gpm
1848/.58 = 3186 rpm

3.14*20.5/12*3186 = 17,090 ft/min tip speed.

Yep, Smartguyz was right, the 48" is 4% faster at 17,700 ft/min, but they are very close. I guess it's the engineer in me that has to see & do the calculations before I'm satisfied.
Tim