Farmerford
Platinum Member
- Joined
- Dec 9, 2006
- Messages
- 733
- Location
- Columbus, Georgia
- Tractor
- Kuborta B2400, L2900, L4330; Caterpillar D3B, John Deere 455D
Scott:
Multiple-spool valves can be configured as parallel, series, tandem, or certain combinations. They all send exactly the same volume and pressure of fluid to a cylinder when only one spool is activated. The difference arises when more than one spool is activated at the same time. For simplicity assume a two spool valve and that when a spool is activated it is fully rather than partially shifted. The differences among the configurations are greatest for a full shift.
The parallel valve allows both circuits to receive fluid directly from the pump at the same time. There is no downstream valve in a parallel system. It is like two sprinkler hoses connected to a "y" connector at the faucet. Fluid can flow to whichever circuit has the lowest backpressure. As a practical matter, if the backpressures in the circuits are close to the same, fluid will flow to both circuits at once.
If an FEL has a parallel valve, when both spools are shifted (say to curl and lift) the bucket cylinders and boom cylinders are all connected to the pump. Oil flows to the cylinders with the lowest resistance (in terms of pressure, not force). If the bucket is empty, on most loaders the bucket will curl fully before the boom moves; once the bucket curls fully and the bucket cylinders stop, they will accept no more fluid and all the fluid then flows to the boom cylinders.
One of my FEL's with parallel valves has an interesting combination of reactions. If I start with the boom down and the bucket parallel to the ground, and then fully shift both valves (they are parallel) the boom lifts about four feet and the bucket does not move (so I assume the boom cylinders have the lowest backpressure), but then the boom stops lifting and the bucket curls fully, and once the bucket curls fully the boom again lifts. In that case, the boom resistance was less than the bucket until the boom raised four feet, then the bucket resistance was less so fluid stopped flowing to the boom and flowed to the bucket until it reached the limit of travel.
I prefer the parallel valve for a FEL because I am lazy (or perhaps just slow witted). When loading loose material with the bucket I can fully shift both the boom and bucket spools and keep them shifted until the boom rises fully and the bucket curls fully. I don't have to feather the valves to send fluid to one circuit or the other; that happens automatically because of the nature of the valve. The fluid flows until both circuits reach their stops. The cylinder sizes, linkage geometry, etc. are such that the bucket curls fully first, then the booms lift the load.
The tandem valve has an upstream valve (receives pump flow first) and a downstream valve (receives pump flow last). When the upstream valve is shifted fully all pump flow is directed to the upstream cylinder and none will go to the downstream cylinder even if it is shifted. If the booms are connected to the upstream valve then when the boom is being lifted (again assuming a fully shifted valve) the bucket will not move since all flow will go to the booms. Once the boom reaches the desired height the boom valve must be returned to neutral in order for the bucket valve to receive fluid.
The series valve has an upstream valve and a downstream valve like the tandem valve, but with an important difference: when the upstream valve is shifted the return flow from the upstream cylinders passes through the downstream valve rather than to the tank. Therefore, if both valves are shifted, the downstream valve receives not fresh fluid from the pump (as it would if the valves were parallel) but rather the exhaust fluid coming out of the upstream cylinder. The advantage is that both valves receive the full volume of flow from the pump and therefore both the boom and the bucket move at the same speed when both valves are shifted that they do when only one is shifted. This is useful when the pump volume is lower than desirable for fast movement.
The series valve has disadvantages. Once the upstream cylinder reaches its limits and stops moving, the downstream cylinder will stop moving also since it depends on the outflow from the upstream cylinder. And since the flow from the pump passes through both sets of cylinders the pump pressure is divided between the cylinders. That is, a 2000 psi pump will not produce the equivalent of 2000 psi of force in both the boom and bucket cylinders at the same time; the total 2000 psi pump pressure will be divided between the cylinders. Thus, if you have a heavy load, the combined resistance of the boom and bucket may be greater than the pressure of the pump, in which case both actions will not happen at once. Finally (and this is the most significant disadvantage to me) the series valve takes more thinking when working with a heavy load: you first try both the boom and the bucket at the same time to see if the pressure is sufficient to move both; if not, then you choose the one to move first and hold the valve in that position until it moves fully; then you shift the valve to the other action until it moves fully. Of course, if the pump pressure is sufficient to move both the boom and bucket at the same time, the cycle time for lift and curl will be much shorter than for a parallel valve since both the boom and bucket are moving at maximum speed.
The tandem and series valve can be made to act (somewhat) like the parallel valve by feathering (partially shifting) the upstream spools. In each case only partially shifting the upstream valve allows some pump flow to pass directly to the downstream valve where it will be directed to the downstream cylinder if the downstream valve is shifted. However, this bypassing fluid suffers a pressure loss passing through the upstream valve equal to the pressure in the upstream cylinder because of the blocking effect of the upstream spool.
Your questions suggest you will make the effort to obtain the time savings from the series valve. We all look forward to receiving a report on how it works for you.
Good luck.
Multiple-spool valves can be configured as parallel, series, tandem, or certain combinations. They all send exactly the same volume and pressure of fluid to a cylinder when only one spool is activated. The difference arises when more than one spool is activated at the same time. For simplicity assume a two spool valve and that when a spool is activated it is fully rather than partially shifted. The differences among the configurations are greatest for a full shift.
The parallel valve allows both circuits to receive fluid directly from the pump at the same time. There is no downstream valve in a parallel system. It is like two sprinkler hoses connected to a "y" connector at the faucet. Fluid can flow to whichever circuit has the lowest backpressure. As a practical matter, if the backpressures in the circuits are close to the same, fluid will flow to both circuits at once.
If an FEL has a parallel valve, when both spools are shifted (say to curl and lift) the bucket cylinders and boom cylinders are all connected to the pump. Oil flows to the cylinders with the lowest resistance (in terms of pressure, not force). If the bucket is empty, on most loaders the bucket will curl fully before the boom moves; once the bucket curls fully and the bucket cylinders stop, they will accept no more fluid and all the fluid then flows to the boom cylinders.
One of my FEL's with parallel valves has an interesting combination of reactions. If I start with the boom down and the bucket parallel to the ground, and then fully shift both valves (they are parallel) the boom lifts about four feet and the bucket does not move (so I assume the boom cylinders have the lowest backpressure), but then the boom stops lifting and the bucket curls fully, and once the bucket curls fully the boom again lifts. In that case, the boom resistance was less than the bucket until the boom raised four feet, then the bucket resistance was less so fluid stopped flowing to the boom and flowed to the bucket until it reached the limit of travel.
I prefer the parallel valve for a FEL because I am lazy (or perhaps just slow witted). When loading loose material with the bucket I can fully shift both the boom and bucket spools and keep them shifted until the boom rises fully and the bucket curls fully. I don't have to feather the valves to send fluid to one circuit or the other; that happens automatically because of the nature of the valve. The fluid flows until both circuits reach their stops. The cylinder sizes, linkage geometry, etc. are such that the bucket curls fully first, then the booms lift the load.
The tandem valve has an upstream valve (receives pump flow first) and a downstream valve (receives pump flow last). When the upstream valve is shifted fully all pump flow is directed to the upstream cylinder and none will go to the downstream cylinder even if it is shifted. If the booms are connected to the upstream valve then when the boom is being lifted (again assuming a fully shifted valve) the bucket will not move since all flow will go to the booms. Once the boom reaches the desired height the boom valve must be returned to neutral in order for the bucket valve to receive fluid.
The series valve has an upstream valve and a downstream valve like the tandem valve, but with an important difference: when the upstream valve is shifted the return flow from the upstream cylinders passes through the downstream valve rather than to the tank. Therefore, if both valves are shifted, the downstream valve receives not fresh fluid from the pump (as it would if the valves were parallel) but rather the exhaust fluid coming out of the upstream cylinder. The advantage is that both valves receive the full volume of flow from the pump and therefore both the boom and the bucket move at the same speed when both valves are shifted that they do when only one is shifted. This is useful when the pump volume is lower than desirable for fast movement.
The series valve has disadvantages. Once the upstream cylinder reaches its limits and stops moving, the downstream cylinder will stop moving also since it depends on the outflow from the upstream cylinder. And since the flow from the pump passes through both sets of cylinders the pump pressure is divided between the cylinders. That is, a 2000 psi pump will not produce the equivalent of 2000 psi of force in both the boom and bucket cylinders at the same time; the total 2000 psi pump pressure will be divided between the cylinders. Thus, if you have a heavy load, the combined resistance of the boom and bucket may be greater than the pressure of the pump, in which case both actions will not happen at once. Finally (and this is the most significant disadvantage to me) the series valve takes more thinking when working with a heavy load: you first try both the boom and the bucket at the same time to see if the pressure is sufficient to move both; if not, then you choose the one to move first and hold the valve in that position until it moves fully; then you shift the valve to the other action until it moves fully. Of course, if the pump pressure is sufficient to move both the boom and bucket at the same time, the cycle time for lift and curl will be much shorter than for a parallel valve since both the boom and bucket are moving at maximum speed.
The tandem and series valve can be made to act (somewhat) like the parallel valve by feathering (partially shifting) the upstream spools. In each case only partially shifting the upstream valve allows some pump flow to pass directly to the downstream valve where it will be directed to the downstream cylinder if the downstream valve is shifted. However, this bypassing fluid suffers a pressure loss passing through the upstream valve equal to the pressure in the upstream cylinder because of the blocking effect of the upstream spool.
Your questions suggest you will make the effort to obtain the time savings from the series valve. We all look forward to receiving a report on how it works for you.
Good luck.
