In a recent hydraulic maintenance workshop, someone asked me my opinion about the isolation valve on the pump intake line and whether it is mandatory to use more expensive ball valves compared to the usually cheaper butterfly valves. The root of this problem lies in the negative effects of turbulence in the pump suction line. The argument for using a ball valve as an isolation valve for the intake line is that when the ball valve is opened, the entire hole of the valve can be used for oil flow. Therefore, if you install a 2-inch ball valve in the 2-inch intake line, when the valve is opened, it will appear to be non-existent (at least from the oil point of view).
On the other hand, the butterfly valve is not full of holes. Even if it is fully opened, the butterfly shape will remain in the hole and show a partial restriction, which is irregular. This can cause turbulence, which may cause dissolved air to escape from the solution in the intake line. If this happens, these bubbles will burst when exposed to pressure at the pump outlet. In other words, butterfly valves may cause cavitation.
So which is the best: ball valve or butterfly valve? Well, like many problems with hydraulics, it depends. In an ideal world, I would always choose the ball valve before the butterfly valve. For an intake pipe with a maximum diameter of 3 inches, there is almost no cost loss in doing so.
But when you get 4 inches, 6 inches and 8 inches in diameter, ball valves are very expensive compared to butterfly valves. They also take up more space, especially over the entire length. Therefore, in mobile applications, for example, not only is the cost of a large-diameter ball valve prohibitively high, but there may not be enough space between the tank outlet and the pump inlet to install it.
There is a third option. Many people mistakenly believe that the intake line isolation valve is essential, but in fact it is not, but there are a few exceptions.
The first question that follows is how to replace the pump if there is no isolation valve on the intake line. There are two answers. First of all, if the pump has a catastrophic failure and your job is “correct”, you should use a filter cart to draw the oil from the tank and pour it into a clean bucket or other suitable container. Then the fuel tank should be cleaned thoroughly, the pump should be replaced, and then the filter cart should be used to pump the oil (assuming it is still usable) back to the tank.
The general objection to this is: “Oh, we don’t have time to do this!” or “There are no 10, 20, or many clean drums around us.” For those who don’t want to do the right job, one solution is to put all Permeate is confined to the head space of the storage tank, and then an industrial vacuum cleaner is connected to the tank vent. When replacing the pump, turn on the vacuum cleaner, and then repeat the operation when the debris from the previous pump failure causes the backup pump to fail.
Of course, there are exceptions, such as drawing more than one pump from the same tank, or pumping 3000 gallons of oil from the tank is just impractical. Sometimes an isolation valve for the intake line is required. If this is the case, it is wise to ensure that they have proximity switches to prevent starting the pump after closing the valve.
My preferred method is to not install ball valves or butterfly valves, if possible. If you must have one, use a ball valve if cost or space are not an issue. However, if any of these problems are a problem, the butterfly valve is the only option.
In many applications, butterfly valves are used as pump intake isolation valves. Large hydraulic excavators are a common example. They have multiple pumps sucking out of the large tank through a large-diameter intake line, and there is not much space-all components that exclude the best option (no valve or ball valve) are excluded.
I don’t remember ever seeing the pump on a large hydraulic excavator not being damaged by at least some cavitation erosion, in which case this damage can be considered considerable wear. Can this cavitation damage be attributed to the turbulence caused by the butterfly valve? Of course it can, but there may be many other reasons. The only way to be sure is to compare two pumps operating under the same conditions-one with a butterfly valve and one without a butterfly valve.
Brendan Casey has more than 20 years of experience in the maintenance, repair and overhaul of mobile and industrial equipment. More information on reducing operating costs and increasing costs…
Post time: Mar-11-2021
