Odd Sizing, Pump Hose to Backhoe valve body

[racerboy832]

I'm all finished with my backhoe thumb. After a few Trips to TSC and 200 + worth of hose and fittings it's up and working. When I was hooking the hoses up, the one line that threw me off was the main pressure line from the pump to the Backhoe valve body. I assumed it was a reg 3/8 like most else. When I got it off the Pump side had a 1/2 Male NPT but it almost looked like a 1/4 hole and on the other side it was a 1/2 female JIC. Did they reduce this that much for a reason? It's a 9GPM pump. The return is a 3/8 line.

 

[racerboy832]

JJ where you @?

 

[BruceWard]

What model tractor or backhoe is this on?

I wonder if it is intended to limit flow and slow the backhoe down?

 

[AKKAMAAN]

3/8" for a 9 gpm return line is way too small size, will create back a lot of back pressure that will eventually make spool valve o-rings leak....
Retracting a double action cylinder, will create a flow up to twice the pump or more flow, depending on piston rod diameter...a 4" bore, 2" rod cylinder will return 133% of pump flow when retracting....9 gpm pump flow will become 12 gpm on return....

To follow common recommendations, 9 gpm require
1/2"+ for pressure (14.7 ft/sec)
5/8"+ for return (9.4 ft/sec)
1"+ for suction (3.7 ft/sec)

(12 gpm return will need 3/4" hose)

Undersized lines and fitting will not reduce flow. It will create pressure and power loss in form of heat.

There are many sizing nomogram available, and the all recommend different max fluid velocity....but still with in the "ball park"...
Here is one of them

You can also use my online spread sheet to calculate the fluid velocity through different sizes of hose.

 

[J_J]

I'm all finished with my backhoe thumb. After a few Trips to TSC and 200 + worth of hose and fittings it's up and working. When I was hooking the hoses up, the one line that threw me off was the main pressure line from the pump to the Backhoe valve body. I assumed it was a reg 3/8 like most else. When I got it off the Pump side had a 1/2 Male NPT but it almost looked like a 1/4 hole and on the other side it was a 1/2 female JIC. Did they reduce this that much for a reason? It's a 9GPM pump. The return is a 3/8 line.

The size of the cyl and the GPM's will dictate speed of operation. Some people like fast for more productive work, and some like slow for more detail work. The cyl are fixed, so about the only thing to do is restrict the flow. If you are good at feathering, you can make it work for you. If you don't like the speed of the BH, and you want faster, change fittings for a larger orifice.

Like others have said, you just about always use larger hose on the return to tank line.

 

[racerboy832]

The cylinders are 2.5" cylinders and the longest stroke is 18" It's a 9gpm pump @ 600RPM. It looks like it was being fed with a 1/4 line with 1/2 ends. It's a Kelly B30F backhoe.

 

[J_J]

You can plug these figures in a hyd calculator from Surplus Hydraulics.

Select hydraulics, then tech help, then calculators, force and speed. Just insert the figures and the unknowns will be computed. This will give you IPS [ in per sec ]. Then divide that into your cyl stroke in inches for cycle time.

I believe AKKAMAAN might have a spread sheet for force and speed.