Slowdown Valves Slowdown valves are bi-directional valves that adjust the speed of oil flow through the valve. In the lowrider industry, we use this valve to adjust how fast the car drops down after you hit the dump switch. PART # PART DESCRIPTION PRICES 620.140 1/4" Street $9.95ea. 620.141 Parker 1/4" Competition $39.95ea. 620.381 Parker 3/8" Competition $49.95ea. SLOWDOWN VALVES_________________________ 1/4 Street Slowdown Valve - $9.95ea. 1/4 Competition Slowdown Valve - $39.95ea. 3/8 Competition Slowdown Valve - $49.95ea. Quantity: