Implemented gravity in pipes when there is no pressure

mechanical/src/main/java/resonantinduction/mechanical/fluid/pipe/PartPipe.java

@@ -117,6 +117,20 @@ public class PartPipe extends PartFramedNode<EnumPipeMaterial, FluidPressureNode
 
                 return false;
             }
+
+            @Override
+            public int getPressure(ForgeDirection dir)
+            {
+                if (super.getPressure(dir) <= 0)
+                {
+                    if (dir == ForgeDirection.UP)
+                        return -2;
+
+                    if (dir == ForgeDirection.DOWN)
+                        return +2;
+                }
+                return super.getPressure(dir);
+            }
         };
 
     }